Methods for forming three-dimensional memory devices

ABSTRACT

In an example, a method for forming a three-dimensional (3D) memory device is disclosed. A semiconductor layer is formed. A memory stack on the semiconductor is formed. A channel structure extending through the memory stack and the semiconductor layer is formed. An end of the channel structure abutting the semiconductor layer is exposed. A portion of the channel structure abutting the semiconductor layer is replaced with a semiconductor plug.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent Ser. No. 16/913,649,filed on Jun. 26, 2020, which is a continuation of International PatentApplication No. PCT/CN2020/092501, filed on May 27, 2020, entitled“METHODS FOR FORMING THREE-DIMENSIONAL MEMORY DEVICES,” both of whichare hereby incorporated by reference in their entireties. Thisapplication is also related to U.S. application Ser. No. 16/913,634,filed on Jun. 26, 2020, entitled “THREE-DIMENSIONAL MEMORY DEVICES,”U.S. application Ser. No. 16/913,611, filed on Jun. 26, 2020, entitled“THREE-DIMENSIONAL MEMORY DEVICES,” and U.S. application Ser. No.16/913,677, filed on Jun. 26, 2020, entitled “METHODS FOR FORMINGTHREE-DIMENSIONAL MEMORY DEVICES,” all of which are hereby incorporatedby reference in their entireties.

BACKGROUND

Embodiments of the present disclosure relate to three-dimensional (3D)memory devices and fabrication methods thereof.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithm, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. The 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

SUMMARY

Embodiments of 3D memory devices and methods for forming the same aredisclosed herein.

In one example, a method for forming a 3D memory device is disclosed. Asacrificial layer on a substrate, an N-type doped semiconductor layer onthe sacrificial layer, and a dielectric stack on the N-type dopedsemiconductor layer are subsequently formed. A channel structureextending vertically through the dielectric stack and the N-type dopedsemiconductor layer is formed. The dielectric stack is replaced with amemory stack, such that the channel structure extends vertically throughthe memory stack and the N-type doped semiconductor layer. The substrateand the sacrificial layer are removed to expose an end of the channelstructure. Part of the channel structure abutting the N-type dopedsemiconductor layer is replaced with a semiconductor plug.

In another example, a method for forming a 3D memory device isdisclosed. A device layer of a silicon on insulator (SOI) waferincluding a handle layer, a buried oxide layer, and the device layer isdoped with an N-type dopant. A dielectric stack is formed on the dopeddevice layer of the SOI wafer. A channel structure extending verticallythrough the dielectric stack and the doped device layer is formed. Thedielectric stack is replaced with a memory stack, such that the channelstructure extends vertically through the memory stack and the dopeddevice layer. The handle layer and the buried oxide layer of the SOIwafer are removed to expose an end of the channel structure. Part of thechannel structure abutting the doped device layer is replaced with asemiconductor plug.

In still another example, a method for forming a 3D memory device isdisclosed. A peripheral circuit is formed on a first substrate. Achannel structure extending vertically through a memory stack and anN-type doped semiconductor layer is formed above a second substrate. Thefirst substrate and the second substrate are bonded in a face-to-facemanner, such that the memory stack is above the peripheral circuit. Thesecond substrate is removed to expose an upper end of the channelstructure. Part of the channel structure abutting the N-type dopedsemiconductor layer is replaced with a semiconductor plug.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a side view of a cross-section of an exemplary 3Dmemory device, according to some embodiments of the present disclosure.

FIG. 2 illustrates a side view of a cross-section of another exemplary3D memory device, according to some embodiments of the presentdisclosure.

FIGS. 3A-3N illustrate a fabrication process for forming an exemplary 3Dmemory device, according to some embodiments of the present disclosure.

FIGS. 4A-4O illustrate a fabrication process for forming anotherexemplary 3D memory device, according to some embodiments of the presentdisclosure.

FIG. 5A illustrates a flowchart of a method for forming an exemplary 3Dmemory device, according to some embodiments of the present disclosure.

FIG. 5B illustrates a flowchart of another method for forming anexemplary 3D memory device, according to some embodiments of the presentdisclosure.

FIG. 6A illustrates a flowchart of a method for forming anotherexemplary 3D memory device, according to some embodiments of the presentdisclosure.

FIG. 6B illustrates a flowchart of another method for forming anotherexemplary 3D memory device, according to some embodiments of the presentdisclosure.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or vertical interconnect access (via)contacts are formed) and one or more dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND memory strings) ona laterally-oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

In some 3D memory devices, such as 3D NAND memory devices, slitstructures (e.g., gate line slits (GLSs)) are used for providingelectrical connections to the source of the memory array, such as arraycommon source (ACS), from the front side of the devices. The front sidesource contacts, however, can affect the electrical performance of the3D memory devices by introducing both leakage current and parasiticcapacitance between the word lines and the source contacts, even withthe presence of spacers in between. The formation of the spacers alsocomplicates the fabrication process. Besides affecting the electricalperformance, the slit structures usually include wall-shaped polysiliconand/or metal fillings, which can introduce local stress to cause waferbow or warp, thereby reducing the production yield.

Moreover, in some 3D NAND memory devices, semiconductor plugs areselectively grown to surround the sidewalls of channel structures, e.g.,known as sidewall selective epitaxial growth (SEG). Compared withanother type of semiconductor plugs that are formed at the lower end ofthe channel structures, e.g., bottom SEG, the formation of sidewall SEGavoids the etching of the memory film and semiconductor channel at thebottom surface of channel holes (also known as “SONO” punch), therebyincreasing the process window, in particular when fabricating 3D NANDmemory devices with advanced technologies, such as having 96 or morelevels with a multi-deck architecture. Sidewall SEGs are usually formedby replacing a sacrificial layer between the substrate and stackstructure with the sidewall SEGs, which involves multiple deposition andetching processes through the slit openings. However, as the levels of3D NAND memory devices continue increasing, the aspect ratio of the slitopenings extending through the stack structure becomes larger, makingthe deposition and etching processes through the slit openings morechallenging and undesirable for forming the sidewall SEGs using theknown approach due to the increased cost and reduced yield.

Various embodiments in accordance with the present disclosure provide 3Dmemory devices with backside source contacts. By moving the sourcecontacts from the front side to the backside, the cost per memory cellcan be reduced as the effective memory cell array area can be increased,and the spacers formation process can be skipped. The device performancecan be improved as well, for example, by avoiding the leakage currentand parasitic capacitance between the word lines and the source contactsand by reducing the local stress caused by the front side slitstructures (as source contacts). The sidewall SEGs (e.g., semiconductorplugs) can be formed from the backside of the substrate to avoid anydeposition or etching process through the openings extending through thestack structure at the front side of the substrate. As a result, thecomplexity and cost of the fabrication process can be reduced, and theproduct yield can be increased. Also, as the fabrication process of thesidewall SEGs is no longer affected by the aspect ratio of the openingsthrough the stack structure, i.e., not limited by the levels of thememory stack, the scalability of the 3D memory devices can be improvedas well.

In some embodiments, the substrate on which the memory stack is formedis removed from the backside to expose the channel structures prior tothe formation of the sidewall SEGs. Thus, the selection of the substratecan be expanded, for example, to dummy wafers to reduce the cost or tosilicon on insulator (SOI) wafers to simplify the fabrication process.The removal of the substrate can also avoid the challenging issue ofthickness uniformity control in known methods using the backsidethinning process.

Various 3D memory device architectures and fabrication methods thereof,for example, with different erase operation mechanisms, are disclosed inthe present disclosure to accommodate different requirements andapplications. In some embodiments, the sidewall SEGs are parts of anN-type doped semiconductor layer to enable gate-induced-drain-leakage(GIDL) erasing by the 3D memory device. In some embodiments, thesidewall SEGs are parts of a P-type doped semiconductor layer to enableP-well bulk erasing by the 3D memory device.

FIG. 1 illustrates a side view of a cross-section of an exemplary 3Dmemory device 100, according to some embodiments of the presentdisclosure. In some embodiments, 3D memory device 100 is a bonded chipincluding a first semiconductor structure 102 and a second semiconductorstructure 104 stacked over first semiconductor structure 102. First andsecond semiconductor structures 102 and 104 are jointed at a bondinginterface 106 therebetween, according to some embodiments. As shown inFIG. 1 , first semiconductor structure 102 can include a substrate 101,which can include silicon (e.g., single crystalline silicon, c-Si),silicon germanium (SiGe), gallium arsenide (GaAs), germanium (Ge), SOI,or any other suitable materials.

First semiconductor structure 102 of 3D memory device 100 can includeperipheral circuits 108 on substrate 101. It is noted that x and y axesare included in FIG. 1 to further illustrate the spatial relationship ofthe components in 3D memory device 100 having substrate 101. Substrate101 includes two lateral surfaces (e.g., a top surface and a bottomsurface) extending laterally in the x-direction (i.e., the lateraldirection). As used herein, whether one component (e.g., a layer or adevice) is “on,” “above,” or “below” another component (e.g., a layer ora device) of a semiconductor device (e.g., 3D memory device 100) isdetermined relative to the substrate of the semiconductor device (e.g.,substrate 101) in they-direction (i.e., the vertical direction) when thesubstrate is positioned in the lowest plane of the semiconductor devicein the y-direction. The same notion for describing spatial relationshipsis applied throughout the present disclosure.

In some embodiments, peripheral circuit 108 is configured to control andsense 3D memory device 100. Peripheral circuit 108 can be any suitabledigital, analog, and/or mixed-signal control and sensing circuits usedfor facilitating the operation of 3D memory device 100 including, butnot limited to, a page buffer, a decoder (e.g., a row decoder and acolumn decoder), a sense amplifier, a driver (e.g., a word line driver),a charge pump, a current or voltage reference, or any active or passivecomponents of the circuit (e.g., transistors, diodes, resistors, orcapacitors). Peripheral circuits 108 can include transistors formed “on”substrate 101, in which the entirety or part of the transistors areformed in substrate 101 (e.g., below the top surface of substrate 101)and/or directly on substrate 101. Isolation regions (e.g., shallowtrench isolations (STIs)) and doped regions (e.g., source regions anddrain regions of the transistors) can be formed in substrate 101 aswell. The transistors are high-speed with advanced logic processes(e.g., technology nodes of 90 nm, 65 nm, 45 nm, 32 nm, 28 nm, 20 nm, 16nm, 14 nm, 10 nm, 7 nm, 5 nm, 3 nm, 2 nm, etc.), according to someembodiments. It is understood that in some embodiments, peripheralcircuit 108 may further include any other circuits compatible with theadvanced logic processes including logic circuits, such as processorsand programmable logic devices (PLDs), or memory circuits, such asstatic random-access memory (SRAM) and dynamic RAM (DRAM).

In some embodiments, first semiconductor structure 102 of 3D memorydevice 100 further includes an interconnect layer (not shown) aboveperipheral circuits 108 to transfer electrical signals to and fromperipheral circuits 108. The interconnect layer can include a pluralityof interconnects (also referred to herein as “contacts”), includinglateral interconnect lines and vertical interconnect access (VIA)contacts. As used herein, the term “interconnects” can broadly includeany suitable types of interconnects, such as middle-end-of-line (MEOL)interconnects and back-end-of-line (BEOL) interconnects. Theinterconnect layer can further include one or more interlayer dielectric(ILD) layers (also known as “intermetal dielectric (IMD) layers”) inwhich the interconnect lines and VIA contacts can form. That is, theinterconnect layer can include interconnect lines and VIA contacts inmultiple ILD layers. The interconnect lines and VIA contacts in theinterconnect layer can include conductive materials including, but notlimited to, tungsten (W), cobalt (Co), copper (Cu), aluminum (Al),silicides, or any combination thereof. The ILD layers in theinterconnect layer can include dielectric materials including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, lowdielectric constant (low-k) dielectrics, or any combination thereof.

As shown in FIG. 1 , first semiconductor structure 102 of 3D memorydevice 100 can further include a bonding layer 110 at bonding interface106 and above the interconnect layer and peripheral circuits 108.Bonding layer 110 can include a plurality of bonding contacts 111 anddielectrics electrically isolating bonding contacts 111. Bondingcontacts 111 can include conductive materials including, but not limitedto, W, Co, Cu, Al, silicides, or any combination thereof. The remainingarea of bonding layer 110 can be formed with dielectrics including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, or any combination thereof. Bonding contacts 111 andsurrounding dielectrics in bonding layer 110 can be used for hybridbonding.

Similarly, as shown in FIG. 1 , second semiconductor structure 104 of 3Dmemory device 100 can also include a bonding layer 112 at bondinginterface 106 and above bonding layer 110 of first semiconductorstructure 102. Bonding layer 112 can include a plurality of bondingcontacts 113 and dielectrics electrically isolating bonding contacts113. Bonding contacts 113 can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The remaining area of bonding layer 112 can be formed withdielectrics including, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, low-k dielectrics, or any combinationthereof. Bonding contacts 113 and surrounding dielectrics in bondinglayer 112 can be used for hybrid bonding. Bonding contacts 113 are incontact with bonding contacts 111 at bonding interface 106, according tosome embodiments.

As described below in detail, second semiconductor structure 104 can bebonded on top of first semiconductor structure 102 in a face-to-facemanner at bonding interface 106. In some embodiments, bonding interface106 is disposed between bonding layers 110 and 112 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 106 is the placeat which bonding layers 112 and 110 are met and bonded. In practice,bonding interface 106 can be a layer with a certain thickness thatincludes the top surface of bonding layer 110 of first semiconductorstructure 102 and the bottom surface of bonding layer 112 of secondsemiconductor structure 104.

In some embodiments, second semiconductor structure 104 of 3D memorydevice 100 further includes an interconnect layer (not shown) abovebonding layer 112 to transfer electrical signals. The interconnect layercan include a plurality of interconnects, such as MEOL interconnects andBEOL interconnects. The interconnect layer can further include one ormore ILD layers in which the interconnect lines and VIA contacts canform. The interconnect lines and VIA contacts in the interconnect layercan include conductive materials including, but not limited to W, Co,Cu, Al, silicides, or any combination thereof. The ILD layers in theinterconnect layer can include dielectric materials including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof.

In some embodiments, 3D memory device 100 is a NAND Flash memory devicein which memory cells are provided in the form of an array of NANDmemory strings. As shown in FIG. 1 , second semiconductor structure 104of 3D memory device 100 can include an array of channel structures 124functioning as the array of NAND memory strings. As shown in FIG. 1 ,each channel structure 124 can extend vertically through a plurality ofpairs each including a conductive layer 116 and a dielectric layer 118.The interleaved conductive layers 116 and dielectric layers 118 are partof a memory stack 114. The number of the pairs of conductive layers 116and dielectric layers 118 in memory stack 114 (e.g., 32, 64, 96, 128,160, 192, 224, 256, or more) determines the number of memory cells in 3Dmemory device 100. It is understood that in some embodiments, memorystack 114 may have a multi-deck architecture (not shown), which includesa plurality of memory decks stacked over one another. The numbers of thepairs of conductive layers 116 and dielectric layers 118 in each memorydeck can be the same or different.

Memory stack 114 can include a plurality of interleaved conductivelayers 116 and dielectric layers 118. Conductive layers 116 anddielectric layers 118 in memory stack 114 can alternate in the verticaldirection. In other words, except the ones at the top or bottom ofmemory stack 114, each conductive layer 116 can be adjoined by twodielectric layers 118 on both sides, and each dielectric layer 118 canbe adjoined by two conductive layers 116 on both sides. Conductivelayers 116 can include conductive materials including, but not limitedto, W, Co, Cu, Al, polysilicon, doped silicon, silicides, or anycombination thereof. Each conductive layer 116 can include a gateelectrode (gate line) surrounded by an adhesive layer and a gatedielectric layer. The gate electrode of conductive layer 116 can extendlaterally as a word line, ending at one or more staircase structures ofmemory stack 114. Dielectric layers 118 can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof.

As shown in FIG. 1 , second semiconductor structure 104 of 3D memorydevice 100 can also include an N-type doped semiconductor layer 120above memory stack 114. N-type doped semiconductor layer 120 can be anexample of the “sidewall SEG” as described above. N-type dopedsemiconductor layer 120 can include a semiconductor material, such assilicon. In some embodiments, N-type doped semiconductor layer 120includes polysilicon formed by deposition techniques, as described belowin detail. In some embodiments, N-type doped semiconductor layer 120includes single crystalline silicon, such as the device layer of an SOIwafer, as described below in detail. N-type doped semiconductor layer120 can be doped with any suitable N-type dopants, such as phosphorus(P), arsenic (Ar), or antimony (Sb), which contribute free electrons andincrease the conductivity of the intrinsic semiconductor. For example,N-type doped semiconductor layer 120 may be a polysilicon layer dopedwith N-type dopant(s), such as P, Ar, or Sb. In some embodiments, N-typedoped semiconductor layer 120 is a single polysilicon layer with auniform doping concentration profile in the vertical direction, asopposed to having multiple polysilicon sub-layers with nonuniform dopingconcentrations at their interfaces (e.g., a sudden doping concentrationchange at an interface between two sub-layers). It is understood thatthe doping concentration of the N-type dopant(s) of N-type dopedsemiconductor layer 120 may still gradually change in the verticaldirection as long as there are not any sudden doping concentrationchanges that can distinguish two or more sub-layers by dopingconcentration variations.

In some embodiments, each channel structure 124 includes a channel holefilled with a semiconductor layer (e.g., as a semiconductor channel 128)and a composite dielectric layer (e.g., as a memory film 126). In someembodiments, semiconductor channel 128 includes silicon, such asamorphous silicon, polysilicon, or single crystalline silicon. In someembodiments, memory film 126 is a composite layer including a tunnelinglayer, a storage layer (also known as a “charge trap layer”), and ablocking layer. The remaining space of channel structure 124 can bepartially or fully filled with a capping layer including dielectricmaterials, such as silicon oxide, and/or an air gap. Channel structure124 can have a cylinder shape (e.g., a pillar shape). The capping layer,semiconductor channel 128, the tunneling layer, storage layer, andblocking layer of memory film 126 are arranged radially from the centertoward the outer surface of the pillar in this order, according to someembodiments. The tunneling layer can include silicon oxide, siliconoxynitride, or any combination thereof. The storage layer can includesilicon nitride, silicon oxynitride, silicon, or any combinationthereof. The blocking layer can include silicon oxide, siliconoxynitride, high-k dielectrics, or any combination thereof. In oneexample, memory film 126 can include a composite layer of siliconoxide/silicon oxynitride/silicon oxide (ONO).

In some embodiments, channel structure 124 further includes a channelplug 129 in the bottom portion (e.g., at the lower end) of channelstructure 124. As used herein, the “upper end” of a component (e.g.,channel structure 124) is the end farther away from substrate 101 in they-direction, and the “lower end” of the component (e.g., channelstructure 124) is the end closer to substrate 101 in the y-directionwhen substrate 101 is positioned in the lowest plane of 3D memory device100. Channel plug 129 can include semiconductor materials (e.g.,polysilicon). In some embodiments, channel plug 129 functions as thedrain of the NAND memory string.

As shown in FIG. 1 , each channel structure 124 can extend verticallythrough interleaved conductive layers 116 and dielectric layers 118 ofmemory stack 114 into N-type doped semiconductor layer 120. The upperend of each channel structure 124 can be flush with or below the topsurface of N-type doped semiconductor layer 120. That is, channelstructure 124 does not extend beyond the top surface of N-type dopedsemiconductor layer 120, according to some embodiments. In someembodiments, the upper end of memory film 126 is below the upper end ofsemiconductor channel 128 in channel structure 124, as shown in FIG. 1 .In some embodiments, the upper end of memory film 126 is below the topsurface of N-type doped semiconductor layer 120, and the upper end ofsemiconductor channel 128 is flush with or below the top surface ofN-type doped semiconductor layer 120. For example, as shown in FIG. 1 ,memory film 126 may end at the bottom surface of N-type dopedsemiconductor layer 120, while semiconductor channel 128 may extendabove the bottom surface of N-type doped semiconductor layer 120, suchthat N-type doped semiconductor layer 120 may surround and in contactwith a top portion 127 of semiconductor channel 128 extending intoN-type doped semiconductor layer 120. In some embodiments, the dopingconcentration of top portion 127 of semiconductor channel 128 extendinginto N-type doped semiconductor layer 120 is different from the dopingconcentration of the rest of semiconductor channel 128. For example,semiconductor channel 128 may include undoped polysilicon except topportion 127, which may include doped polysilicon to increase itsconductivity in forming an electrical connection with the surroundingN-type doped semiconductor layer 120.

In some embodiments, N-type doped semiconductor layer 120 includessemiconductor plugs 122 each surrounding and in contact with top portion127 of respective semiconductor channel 128 of channel structure 124extending into N-type doped semiconductor layer 120. Semiconductor plug122 includes doped polysilicon, for example, N-type doped polysilicon,according to some embodiments. The doping concentration of semiconductorplugs 122 can be different from the doping concentration of the rest ofN-type doped semiconductor layer 120 since semiconductor plugs 122 canbe formed in a later process after the formation of the rest of N-typedoped semiconductor layer 120, as described below in detail. In someembodiments, semiconductor plugs 122 include polysilicon (e.g., N-typedoped polysilicon), and the rest of N-type doped semiconductor layer 120includes single crystalline silicon (e.g., N-type doped singlecrystalline silicon). In some embodiments, semiconductor plugs 122include polysilicon (e.g., N-type doped polysilicon), and the rest ofN-type doped semiconductor layer 120 includes polysilicon (e.g., N-typedoped polysilicon), but with doping centration different from that ofsemiconductor plugs 122.

Each semiconductor plug 122 can surround and in contact with thesidewall of top portion 127 of respective semiconductor channel 128. Asa result, semiconductor plugs 122 in N-type doped semiconductor layer120 can work as a “sidewall SEG (e.g., semiconductor plug)” of channelstructure 124 to replace the “bottom SEG (e.g., semiconductor plug).”Moreover, as described below in detail, the formation of semiconductorplugs 122 occurs at the opposite side of memory stack 114, which canavoid any deposition or etching process through openings extendingthrough memory stack 114, thereby reducing the fabrication complexityand cost and increasing the yield and vertical scalability. Depending onthe relative position of the upper end of semiconductor channel 128 ofeach channel structure 124 with respect to the top surface of N-typedoped semiconductor layer 120, semiconductor plug 122 may be formedabove and in contact with the upper end of semiconductor channel 128 aswell, for example, as shown in FIG. 1 , when the upper end ofsemiconductor channel 128 is below the top surface of N-type dopedsemiconductor layer 120. It is understood that in other examples inwhich the upper end of semiconductor channel 128 is flush with the topsurface of N-type doped semiconductor layer 120, semiconductor plug 122may be formed surrounding and in contact with the sidewall of topportion 127 of semiconductor channel 128 only.

Nevertheless, N-type doped semiconductor layer 120 surrounding topportion 127 of semiconductor channels 128 of channel structures 124 withsemiconductor plugs 122 (e.g., as sidewall SEGs) can enableGIDL-assisted body biasing for erase operations for 3D memory device100. The GIDL around the source select gate of the NAND memory stringcan generate hole current into the NAND memory string to raise the bodypotential for erase operations.

As shown in FIG. 1 , second semiconductor structure 104 of 3D memorydevice 100 can further include insulating structures 130 each extendingvertically through interleaved conductive layers 116 and dielectriclayers 118 of memory stack 114. Different from channel structure 124that extends further into N-type doped semiconductor layer 120,insulating structures 130 stops at the bottom surface of N-type dopedsemiconductor layer 120, i.e., does not extend vertically into N-typedoped semiconductor layer 120, according to some embodiments. That is,the top surface of insulating structure 130 can be flush with the bottomsurface of N-type doped semiconductor layer 120. Each insulatingstructure 130 can also extend laterally to separate channel structures124 into a plurality of blocks. That is, memory stack 114 can be dividedinto a plurality of memory blocks by insulating structures 130, suchthat the array of channel structures 124 can be separated into eachmemory block. Different from the slit structures in existing 3D NANDmemory devices described above, which include front side ACS contacts,insulating structure 130 does not include any contact therein (i.e., notfunctioning as the source contact) and thus, does not introduceparasitic capacitance and leakage current with conductive layers 116(including word lines), according to some embodiments. In someembodiments, each insulating structure 130 includes an opening (e.g., aslit) filled with one or more dielectric materials, including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, or anycombination thereof. In one example, each insulating structure 130 maybe filled with silicon oxide.

Moreover, as described below in detail, because the opening for forminginsulating structure 130 is not used for forming N-type dopedsemiconductor layer 120 and semiconductor plugs 122 therein (e.g., assidewall SEGs), the increased aspect ratio of the opening as the numberof interleaved conductive layers 116 and dielectric layers 118 increaseswould not affect the formation of N-type doped semiconductor layer 120and semiconductor plugs 122 therein.

Instead of the front side source contacts, 3D memory device 100 caninclude a backside source contact 132 above memory stack 114 and incontact with N-type doped semiconductor layer 120, as shown in FIG. 1 .Source contact 132 and memory stack 114 (and insulating structure 130therethrough) can be disposed at opposites sides of N-type dopedsemiconductor layer 120 and thus, viewed as a “backside” source contact.In some embodiments, source contact 132 is electrically connected tosemiconductor channel 128 of channel structure 124 through semiconductorplug 122 of N-type doped semiconductor layer 120. In some embodiments,source contact 132 is not laterally aligned with insulating structure130, but approximate to channel structure 124 to reduce the resistanceof the electrical connection therebetween. For example, source contact132 may be laterally between insulating structure 130 and channelstructure 124 (e.g., in the x-direction in FIG. 1 ). Source contacts 132can include any suitable types of contacts. In some embodiments, sourcecontacts 132 include a VIA contact. In some embodiments, source contacts132 include a wall-shaped contact extending laterally. Source contact132 can include one or more conductive layers, such as a metal layer(e.g., W, Co, Cu, or Al) or a silicide layer surrounded by an adhesivelayer (e.g., titanium nitride (TiN)).

As shown in FIG. 1 , 3D memory device 100 can further include a BEOLinterconnect layer 133 above and electrically connected to sourcecontact 132 for pad-out, e.g., transferring electrical signals between3D memory device 100 and external circuits. In some embodiments,interconnect layer 133 includes one or more ILD layers 134 on N-typedoped semiconductor layer 120 and a redistribution layer 136 on ILDlayers 134. The upper end of source contact 132 is flush with the topsurface of ILD layers 134, and the bottom surface of redistributionlayer 136, and source contact 132 extends vertically through ILD layers134 into N-type doped semiconductor layer 120, according to someembodiments. ILD layers 134 in interconnect layer 133 can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, silicon oxynitride, low-k dielectrics, or anycombination thereof. Redistribution layer 136 in interconnect layer 133can include conductive materials including, but not limited to W, Co,Cu, Al, silicides, or any combination thereof. In one example,redistribution layer 136 includes Al. In some embodiments, interconnectlayer 133 further includes a passivation layer 138 as the outmost layerfor passivation and protection of 3D memory device 100. Part ofredistribution layer 136 can be exposed from passivation layer 138 ascontact pads 140. That is, interconnect layer 133 of 3D memory device100 can also include contact pads 140 for wire bonding and/or bondingwith an interposer.

In some embodiments, second semiconductor structure 104 of 3D memorydevice 100 further includes contacts 142 and 144 through N-type dopedsemiconductor layer 120. As N-type doped semiconductor layer 120 can bea thinned substrate, for example, the device layer of an SOI wafer,contacts 142 and 144 are through silicon contacts (TSCs), according tosome embodiments. In some embodiments, contact 142 extends throughN-type doped semiconductor layer 120 and ILD layers 134 to be in contactwith redistribution layer 136, such that N-type doped semiconductorlayer 120 is electrically connected to contact 142 through sourcecontact 132 and redistribution layer 136 of interconnect layer 133. Insome embodiments, contact 144 extends through N-type doped semiconductorlayer 120 and ILD layers 134 to be in contact with contact pad 140.Contacts 142 and 144 each can include one or more conductive layers,such as a metal layer (e.g., W, Co, Cu, or Al) or a silicide layersurrounded by an adhesive layer (e.g., TiN). In some embodiments, atleast contact 144 further includes a spacer (e.g., a dielectric layer)to electrically separate contact 144 from N-type doped semiconductorlayer 120.

In some embodiments, 3D memory device 100 further includes peripheralcontacts 146 and 148 each extending vertically outside of memory stack114. Each peripheral contact 146 or 148 can have a depth greater thanthe depth of memory stack 114 to extend vertically from bonding layer112 to N-type doped semiconductor layer 120 in a peripheral region thatis outside of memory stack 114. In some embodiments, peripheral contact146 is below and in contact with contact 142, such that N-type dopedsemiconductor layer 120 is electrically connected to peripheral circuit108 in first semiconductor structure 102 through at least source contact132, interconnect layer 133, contact 142, and peripheral contact 146. Insome embodiments, peripheral contact 148 is below and in contact withcontact 144, such that peripheral circuit 108 in first semiconductorstructure 102 is electrically connected to contact pad 140 for pad-outthrough at least contact 144 and peripheral contact 148. Peripheralcontacts 146 and 148 each can include one or more conductive layers,such as a metal layer (e.g., W, Co, Cu, or Al) or a silicide layersurrounded by an adhesive layer (e.g., TiN).

As shown in FIG. 1 , 3D memory device 100 also includes a variety oflocal contacts (also known as “Cl”) as part of the interconnectstructure, which are in contact with a structure in memory stack 114directly. In some embodiments, the local contacts include channel localcontacts 150 each below and in contact with the lower end of respectivechannel structure 124. Each channel local contact 150 can beelectrically connected to a bit line contact (not shown) for bit linefan-out. In some embodiments, the local contacts further include wordline local contacts 152 each below and in contact with respectiveconductive layer 116 (including a word line) at the staircase structureof memory stack 114 for word line fan-out. Local contacts, such aschannel local contacts 150 and word line local contacts 152, can beelectrically connected to peripheral circuits 108 of first semiconductorstructure 102 through at least bonding layers 112 and 110. Localcontacts, such as channel local contacts 150 and word line localcontacts 152, each can include one or more conductive layers, such as ametal layer (e.g., W, Co, Cu, or Al) or a silicide layer surrounded byan adhesive layer (e.g., TiN).

FIG. 2 illustrates a side view of a cross-section of another exemplary3D memory device 200, according to some embodiments of the presentdisclosure. In some embodiments, 3D memory device 200 is a bonded chipincluding a first semiconductor structure 202 and a second semiconductorstructure 204 stacked over first semiconductor structure 202. First andsecond semiconductor structures 202 and 204 are jointed at a bondinginterface 206 therebetween, according to some embodiments. As shown inFIG. 2 , first semiconductor structure 202 can include a substrate 201,which can include silicon (e.g., single crystalline silicon, c-Si),SiGe, GaAs, Ge, SOI, or any other suitable materials.

First semiconductor structure 202 of 3D memory device 200 can includeperipheral circuits 208 on substrate 201. In some embodiments,peripheral circuit 208 is configured to control and sense 3D memorydevice 200. Peripheral circuit 208 can be any suitable digital, analog,and/or mixed-signal control and sensing circuits used for facilitatingthe operation of 3D memory device 200 including, but not limited to, apage buffer, a decoder (e.g., a row decoder and a column decoder), asense amplifier, a driver (e.g., a word line driver), a charge pump, acurrent or voltage reference, or any active or passive components of thecircuit (e.g., transistors, diodes, resistors, or capacitors).Peripheral circuits 208 can include transistors formed “on” substrate201, in which the entirety or part of the transistors are formed insubstrate 201 (e.g., below the top surface of substrate 201) and/ordirectly on substrate 201. Isolation regions (e.g., shallow trenchisolations (STIs)) and doped regions (e.g., source regions and drainregions of the transistors) can be formed in substrate 201 as well. Thetransistors are high-speed with advanced logic processes (e.g.,technology nodes of 90 nm, 65 nm, 45 nm, 32 nm, 28 nm, 20 nm, 16 nm, 14nm, 10 nm, 7 nm, 5 nm, 3 nm, 2 nm, etc.), according to some embodiments.It is understood that in some embodiments, peripheral circuit 208 mayfurther include any other circuits compatible with the advanced logicprocesses including logic circuits, such as processors and PLDs, ormemory circuits, such as SRAM and DRAM.

In some embodiments, first semiconductor structure 202 of 3D memorydevice 200 further includes an interconnect layer (not shown) aboveperipheral circuits 208 to transfer electrical signals to and fromperipheral circuits 208. The interconnect layer can include a pluralityof interconnects (also referred to herein as “contacts”), includinglateral interconnect lines and VIA contacts. As used herein, the term“interconnects” can broadly include any suitable types of interconnects,such as MEOL interconnects and BEOL interconnects. The interconnectlayer can further include one or more ILD layers (also known as “(IMDlayers”) in which the interconnect lines and VIA contacts can form. Thatis, the interconnect layer can include interconnect lines and VIAcontacts in multiple ILD layers. The interconnect lines and VIA contactsin the interconnect layer can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The ILD layers in the interconnect layer can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,silicon oxynitride, low-k dielectrics, or any combination thereof.

As shown in FIG. 2 , first semiconductor structure 202 of 3D memorydevice 200 can further include a bonding layer 210 at bonding interface206 and above the interconnect layer and peripheral circuits 208.Bonding layer 210 can include a plurality of bonding contacts 211 anddielectrics electrically isolating bonding contacts 211. Bondingcontacts 211 can include conductive materials including, but not limitedto, W, Co, Cu, Al, silicides, or any combination thereof. The remainingarea of bonding layer 210 can be formed with dielectrics including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, or any combination thereof. Bonding contacts 211 andsurrounding dielectrics in bonding layer 210 can be used for hybridbonding.

Similarly, as shown in FIG. 2 , second semiconductor structure 204 of 3Dmemory device 200 can also include a bonding layer 212 at bondinginterface 206 and above bonding layer 210 of first semiconductorstructure 202. Bonding layer 212 can include a plurality of bondingcontacts 213 and dielectrics electrically isolating bonding contacts213. Bonding contacts 213 can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The remaining area of bonding layer 212 can be formed withdielectrics including, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, low-k dielectrics, or any combinationthereof. Bonding contacts 213 and surrounding dielectrics in bondinglayer 212 can be used for hybrid bonding. Bonding contacts 213 are incontact with bonding contacts 211 at bonding interface 206, according tosome embodiments.

As described below in detail, second semiconductor structure 204 can bebonded on top of first semiconductor structure 202 in a face-to-facemanner at bonding interface 206. In some embodiments, bonding interface206 is disposed between bonding layers 210 and 212 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 206 is the placeat which bonding layers 212 and 210 are met and bonded. In practice,bonding interface 206 can be a layer with a certain thickness thatincludes the top surface of bonding layer 210 of first semiconductorstructure 202 and the bottom surface of bonding layer 212 of secondsemiconductor structure 204.

In some embodiments, second semiconductor structure 204 of 3D memorydevice 200 further includes an interconnect layer (not shown) abovebonding layer 212 to transfer electrical signals. The interconnect layercan include a plurality of interconnects, such as MEOL interconnects andBEOL interconnects. The interconnect layer can further include one ormore ILD layers in which the interconnect lines and VIA contacts canform. The interconnect lines and VIA contacts in the interconnect layercan include conductive materials including, but not limited to W, Co,Cu, Al, silicides, or any combination thereof. The ILD layers in theinterconnect layer can include dielectric materials including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, low-kdielectrics, or any combination thereof.

In some embodiments, 3D memory device 200 is a NAND Flash memory devicein which memory cells are provided in the form of an array of NANDmemory strings. As shown in FIG. 2 , second semiconductor structure 204of 3D memory device 200 can include an array of channel structures 224functioning as the array of NAND memory strings. As shown in FIG. 2 ,each channel structure 224 can extend vertically through a plurality ofpairs each including a conductive layer 216 and a dielectric layer 218.The interleaved conductive layers 216 and dielectric layers 218 are partof a memory stack 214. The number of the pairs of conductive layers 216and dielectric layers 218 in memory stack 214 (e.g., 32, 64, 96, 128,160, 192, 224, 256, or more) determines the number of memory cells in 3Dmemory device 200. It is understood that in some embodiments, memorystack 214 may have a multi-deck architecture (not shown), which includesa plurality of memory decks stacked over one another. The numbers of thepairs of conductive layers 216 and dielectric layers 218 in each memorydeck can be the same or different.

Memory stack 214 can include a plurality of interleaved conductivelayers 216 and dielectric layers 218. Conductive layers 216 anddielectric layers 218 in memory stack 214 can alternate in the verticaldirection. In other words, except the ones at the top or bottom ofmemory stack 214, each conductive layer 216 can be adjoined by twodielectric layers 218 on both sides, and each dielectric layer 218 canbe adjoined by two conductive layers 216 on both sides. Conductivelayers 216 can include conductive materials including, but not limitedto, W, Co, Cu, Al, polysilicon, doped silicon, silicides, or anycombination thereof. Each conductive layer 216 can include a gateelectrode (gate line) surrounded by an adhesive layer and a gatedielectric layer. The gate electrode of conductive layer 216 can extendlaterally as a word line, ending at one or more staircase structures ofmemory stack 214. Dielectric layers 218 can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof.

As shown in FIG. 2 , second semiconductor structure 204 of 3D memorydevice 200 can also include a P-type doped semiconductor layer 220 abovememory stack 114. P-type doped semiconductor layer 220 can be an exampleof the “sidewall SEG” as described above. P-type doped semiconductorlayer 220 can include a semiconductor material, such as silicon. In someembodiments, P-type doped semiconductor layer 220 includes polysiliconformed by deposition techniques, as described below in detail. In someembodiments, P-type doped semiconductor layer 220 includes singlecrystalline silicon, such as the device layer of an SOI wafer, asdescribed below in detail. P-type doped semiconductor layer 220 can bedoped with any suitable P-type dopants, such as boron (B), gallium (Ga),or aluminum (Al), to an intrinsic semiconductor creates deficiencies ofvalence electrons, called “holes.” For example, P-type dopedsemiconductor layer 220 may be a polysilicon layer doped with P-typedopant(s), such as P, Ar, or Sb. In some embodiments, P-type dopedsemiconductor layer 220 is a single polysilicon layer with a uniformdoping concentration profile in the vertical direction, as opposed tohaving multiple polysilicon sub-layers with nonuniform dopingconcentrations at their interfaces (e.g., a sudden doping concentrationchange at an interface between two sub-layers). It is understood thatthe doping concentration of the P-type dopant(s) of P-type dopedsemiconductor layer 220 may still gradually change in the verticaldirection as long as there are not any sudden doping concentrationchanges that can distinguish two or more sub-layers by dopingconcentration variations.

In some embodiments, second semiconductor structure 204 of 3D memorydevice 200 further includes an N-well 221 in P-type doped semiconductorlayer 220. N-well 221 can be doped with any suitable N-type dopants,such as P, Ar, or Sb, which contribute free electrons and increase theconductivity of the intrinsic semiconductor. In some embodiments, N-well221 is doped from the bottom surface of P-type doped semiconductor layer220. It is understood that N-well 221 may extend vertically in theentire thickness of P-type doped semiconductor layer 220, i.e., to thetop surface of P-type doped semiconductor layer 220, or part of theentire thickness of P-type doped semiconductor layer 220.

In some embodiments, each channel structure 224 includes a channel holefilled with a semiconductor layer (e.g., as a semiconductor channel 228)and a composite dielectric layer (e.g., as a memory film 226). In someembodiments, semiconductor channel 228 includes silicon, such asamorphous silicon, polysilicon, or single crystalline silicon. In someembodiments, memory film 226 is a composite layer including a tunnelinglayer, a storage layer (also known as a “charge trap layer”), and ablocking layer. The remaining space of channel structure 224 can bepartially or fully filled with a capping layer including dielectricmaterials, such as silicon oxide, and/or an air gap. Channel structure224 can have a cylinder shape (e.g., a pillar shape). The capping layer,semiconductor channel 228, the tunneling layer, storage layer, andblocking layer of memory film 226 are arranged radially from the centertoward the outer surface of the pillar in this order, according to someembodiments. The tunneling layer can include silicon oxide, siliconoxynitride, or any combination thereof. The storage layer can includesilicon nitride, silicon oxynitride, silicon, or any combinationthereof. The blocking layer can include silicon oxide, siliconoxynitride, high-k dielectrics, or any combination thereof. In oneexample, memory film 226 can include a composite layer of siliconoxide/silicon oxynitride/silicon oxide (ONO).

In some embodiments, channel structure 224 further includes a channelplug 227 in the bottom portion (e.g., at the lower end) of channelstructure 224. As used herein, the “upper end” of a component (e.g.,channel structure 224) is the end farther away from substrate 201 in they-direction, and the “lower end” of the component (e.g., channelstructure 224) is the end closer to substrate 201 in the y-directionwhen substrate 201 is positioned in the lowest plane of 3D memory device200. Channel plug 227 can include semiconductor materials (e.g.,polysilicon). In some embodiments, channel plug 227 functions as thedrain of the NAND memory string.

As shown in FIG. 2 , each channel structure 224 can extend verticallythrough interleaved conductive layers 216 and dielectric layers 218 ofmemory stack 214 into P-type doped semiconductor layer 220. The upperend of each channel structure 224 can be flush with or below the topsurface of P-type doped semiconductor layer 220. That is, channelstructure 224 does not extend beyond the top surface of P-type dopedsemiconductor layer 220, according to some embodiments. In someembodiments, the upper end of memory film 226 is below the upper end ofsemiconductor channel 228 in channel structure 224, as shown in FIG. 2 .In some embodiments, the upper end of memory film 226 is below the topsurface of P-type doped semiconductor layer 220, and the upper end ofsemiconductor channel 228 is flush with or below the top surface ofP-type doped semiconductor layer 220. For example, as shown in FIG. 2 ,memory film 226 may end at the bottom surface of P-type dopedsemiconductor layer 220, while semiconductor channel 228 may extendabove the bottom surface of P-type doped semiconductor layer 220, suchthat P-type doped semiconductor layer 220 may surround and in contactwith a top portion 229 of semiconductor channel 228 extending intoP-type doped semiconductor layer 220. In some embodiments, the dopingconcentration of top portion 229 of semiconductor channel 228 extendinginto P-type doped semiconductor layer 220 is different from the dopingconcentration of the rest of semiconductor channel 228. For example,semiconductor channel 228 may include undoped polysilicon except topportion 229, which may include doped polysilicon to increase itsconductivity in forming an electrical connection with surrounding P-typedoped semiconductor layer 220.

In some embodiments, P-type doped semiconductor layer 220 includessemiconductor plugs 222 each surrounding and in contact with top portion229 of respective semiconductor channel 228 of channel structure 224extending into P-type doped semiconductor layer 220. Semiconductor plug222 includes doped polysilicon, for example, P-type doped polysilicon,according to some embodiments. The doping concentration of semiconductorplugs 222 can be different from the doping concentration of the rest ofP-type doped semiconductor layer 220 since semiconductor plugs 222 canbe formed in a later process after the formation of the rest of P-typedoped semiconductor layer 220, as described below in detail. In someembodiments, semiconductor plugs 222 include polysilicon (e.g., P-typedoped polysilicon), and the rest of P-type doped semiconductor layer 220includes single crystalline silicon (e.g., P-type doped singlecrystalline silicon). In some embodiments, semiconductor plugs 222include polysilicon (e.g., P-type doped polysilicon), and the rest ofP-type doped semiconductor layer 220 includes polysilicon (e.g., P-typedoped polysilicon), but with doping centration different from that ofsemiconductor plugs 222.

Each semiconductor plug 222 can surround and in contact with thesidewall of top portion 229 of respective semiconductor channel 228. Asa result, semiconductor plugs 222 in P-type doped semiconductor layer220 can work as a “sidewall SEG (e.g., semiconductor plug)” of channelstructure 224 to replace the “bottom SEG (e.g., semiconductor plug).”Moreover, as described below in detail, the formation of semiconductorplugs 222 occurs at the opposite side of memory stack 214, which canavoid any deposition or etching process through openings extendingthrough memory stack 214, thereby reducing the fabrication complexityand cost and increasing the yield and vertical scalability. Depending onthe relative position of the upper end of semiconductor channel 228 ofeach channel structure 224 with respect to the top surface of P-typedoped semiconductor layer 220, semiconductor plug 222 may be formedabove and in contact with the upper end of semiconductor channel 228 aswell, for example, as shown in FIG. 2 , when the upper end ofsemiconductor channel 228 is below the top surface of P-type dopedsemiconductor layer 220. It is understood that in other examples inwhich the upper end of semiconductor channel 228 is flush with the topsurface of P-type doped semiconductor layer 220, semiconductor plug 222may be formed surrounding and in contact with the sidewall of topportion 229 of semiconductor channel 228 only.

Nevertheless, P-type doped semiconductor layer 220 surrounding topportion 229 of semiconductor channels 228 of channel structures 224 withsemiconductor plugs 222 (e.g., as sidewall SEGs) can enable P-well bulkerase operations for 3D memory device 200. The design of the 3D memorydevice 200 disclosed herein can achieve the separation of the holecurrent path and the electron current path for forming erase operationsand read operations, respectively. In some embodiments, 3D memory device200 is configured to form an electron current path between the electronsource (e.g., N-well 221) and semiconductor channel 228 of channelstructure 224 to provide electrons to the NAND memory string whenperforming a read operation, according to some embodiments. Conversely,3D memory device 200 is configured to form a hole current path betweenthe hole source (e.g., P-type doped semiconductor layer 220) andsemiconductor channel 228 of channel structure 224 to provide holes tothe NAND memory string when performing a P-well bulk erase operation,according to some embodiments.

As shown in FIG. 2 , second semiconductor structure 204 of 3D memorydevice 200 can further include insulating structures 230 each extendingvertically through interleaved conductive layers 216 and dielectriclayers 218 of memory stack 214. Different from channel structure 224that extends further into P-type doped semiconductor layer 220,insulating structures 230 stops at the bottom surface of P-type dopedsemiconductor layer 220, i.e., does not extend vertically into P-typedoped semiconductor layer 220, according to some embodiments. That is,the top surface of insulating structure 230 can be flush with the bottomsurface of P-type doped semiconductor layer 220. Each insulatingstructure 230 can also extend laterally to separate channel structures224 into a plurality of blocks. That is, memory stack 214 can be dividedinto a plurality of memory blocks by insulating structures 230, suchthat the array of channel structures 224 can be separated into eachmemory block. Different from the slit structures in existing 3D NANDmemory devices described above, which include front side ACS contacts,insulating structure 230 does not include any contact therein (i.e., notfunctioning as the source contact) and thus, does not introduceparasitic capacitance and leakage current with conductive layers 216(including word lines), according to some embodiments. In someembodiments, each insulating structure 230 includes an opening (e.g., aslit) filled with one or more dielectric materials, including, but notlimited to, silicon oxide, silicon nitride, silicon oxynitride, or anycombination thereof. In one example, each insulating structure 230 maybe filled with silicon oxide.

Moreover, as described below in detail, because the opening for forminginsulating structure 230 is not used for forming P-type dopedsemiconductor layer 220 and semiconductor plugs 222 therein (e.g., assidewall SEGs), the increased aspect ratio of the opening as the numberof interleaved conductive layers 216 and dielectric layers 218 increaseswould not affect the formation of P-type doped semiconductor layer 220and semiconductor plugs 222 therein.

Instead of the front side source contacts, 3D memory device 100 caninclude backside source contacts 231 and 232 above memory stack 214 andin contact with N-well 221 and P-type doped semiconductor layer 220,respectively, as shown in FIG. 1 . Source contacts 231 and 232 andmemory stack 214 (and insulating structure 230 therethrough) can bedisposed at opposites sides of P-type doped semiconductor layer 220 andthus, viewed as “backside” source contacts. In some embodiments, sourcecontact 232 in contact with P-type doped semiconductor layer 220 iselectrically connected to semiconductor channel 228 of channel structure224 through semiconductor plug 222 of P-type doped semiconductor layer220. In some embodiments, source contact 231 in contact with N-well 221is electrically connected to semiconductor channel 228 of channelstructure 224 through semiconductor plug 222 of P-type dopedsemiconductor layer 220. In some embodiments, source contact 232 is notlaterally aligned with insulating structure 230 and is approximate tochannel structure 224 to reduce the resistance of the electricalconnection therebetween. It is understood that although source contact231 is laterally aligned with insulating structure 230 as shown in FIG.2 , in some examples, source contact 231 may not be laterally alignedwith insulating structure 230, but approximate to channel structure 224(e.g., laterally between insulating structure 230 and channel structure224) to reduce the resistance of the electrical connection therebetweenas well. As described above, source contacts 231 and 232 can be used toseparately control the electron current and hole current during the readoperations and erase operations, respectively. Source contacts 231 and232 can include any suitable types of contacts. In some embodiments,source contacts 231 and 232 include a VIA contact. In some embodiments,source contacts 231 and 232 include a wall-shaped contact extendinglaterally. Source contacts 231 and 232 can include one or moreconductive layers, such as a metal layer (e.g., W, Co, Cu, or Al) or asilicide layer surrounded by an adhesive layer (e.g., titanium nitride(TiN)).

As shown in FIG. 2 , 3D memory device 100 can further include a BEOLinterconnect layer 233 above and electrically connected to sourcecontacts 231 and 232 for pad-out, e.g., transferring electrical signalsbetween 3D memory device 200 and external circuits. In some embodiments,interconnect layer 233 includes one or more ILD layers 234 on P-typedoped semiconductor layer 220 and a redistribution layer 236 on ILDlayers 234. The upper end of source contact 231 or 232 is flush with thetop surface of ILD layers 234 and the bottom surface of redistributionlayer 236. Source contacts 231 and 232 can be electrically separated byon ILD layers 234. In some embodiments, source contact 232 extendsvertically through ILD layers 234 into P-type doped semiconductor layer220 to make an electrical connection with P-type doped semiconductorlayer 220. In some embodiments, source contact 231 extends verticallythrough ILD layers 234 and P-type doped semiconductor layer 220 intoN-well 221 to make an electrical connection with N-well. Source contact231 can include a spacer (e.g., a dielectric layer) surrounding itssidewall to be electrically separated from P-type doped semiconductorlayer 220. Redistribution layer 236 can include two electricallyseparated interconnects: a first interconnect 236-1 in contact withsource contact 232 and a second interconnect 236-2 in contact withsource contact 231.

ILD layers 234 in interconnect layer 233 can include dielectricmaterials including, but not limited to, silicon oxide, silicon nitride,silicon oxynitride, low-k dielectrics, or any combination thereof.Redistribution layer 236 in interconnect layer 233 can includeconductive materials including, but not limited to W, Co, Cu, Al,silicides, or any combination thereof. In one example, redistributionlayer 236 includes Al. In some embodiments, interconnect layer 233further includes a passivation layer 238 as the outmost layer forpassivation and protection of 3D memory device 200. Part ofredistribution layer 236 can be exposed from passivation layer 238 ascontact pads 240. That is, interconnect layer 233 of 3D memory device200 can also include contact pads 240 for wire bonding and/or bondingwith an interposer.

In some embodiments, second semiconductor structure 204 of 3D memorydevice 200 further includes contacts 242, 243, and 244 through P-typedoped semiconductor layer 220. As P-type doped semiconductor layer 220can be a thinned substrate, for example, the device layer of a SOIwafer, contacts 242, 243, and 244 are TSCs, according to someembodiments. In some embodiments, contact 242 extends through P-typedoped semiconductor layer 220 and ILD layers 234 to be in contact withfirst interconnect 236-1 of redistribution layer 236, such that P-typedoped semiconductor layer 220 is electrically connected to contact 242through source contact 232 and first interconnect 236-1 of interconnectlayer 233. In some embodiments, contact 243 extends through P-type dopedsemiconductor layer 220 and ILD layers 234 to be in contact with secondinterconnect 236-2 of redistribution layer 236, such that N-well 221 iselectrically connected to contact 243 through source contact 231 andsecond interconnect 236-2 of interconnect layer 233. In someembodiments, contact 244 extends through P-type doped semiconductorlayer 220 and ILD layers 234 to be in contact with contact pad 240.Contacts 242, 243, and 244 each can include one or more conductivelayers, such as a metal layer (e.g., W, Co, Cu, or Al) or a silicidelayer surrounded by an adhesive layer (e.g., TiN). In some embodiments,at least contacts 243 and 244 each further include a spacer (e.g., adielectric layer) to electrically separate contacts 243 and 244 fromP-type doped semiconductor layer 220.

In some embodiments, 3D memory device 200 further includes peripheralcontacts 246, 247, and 248 each extending vertically outside of memorystack 214. Each peripheral contact 246, 247, or 248 can have a depthgreater than the depth of memory stack 214 to extend vertically frombonding layer 212 to P-type doped semiconductor layer 220 in aperipheral region that is outside of memory stack 214. In someembodiments, peripheral contact 246 is below and in contact with contact242, such that P-type doped semiconductor layer 220 is electricallyconnected to peripheral circuit 208 in first semiconductor structure 202through at least source contact 232, first interconnect 236-1 ofinterconnect layer 233, contact 242, and peripheral contact 246. In someembodiments, peripheral contact 247 is below and in contact with contact243, such that N-well 221 is electrically connected to peripheralcircuit 208 in first semiconductor structure 202 through at least sourcecontact 231, second interconnect 236-2 of interconnect layer 233,contact 243, and peripheral contact 247. That is, the electron currentand hole current for read operations and erase operations can beseparately controlled by peripheral circuits 208 through differentelectrical connections. In some embodiments, peripheral contact 248 isbelow and in contact with contact 244, such that peripheral circuit 208in first semiconductor structure 202 is electrically connected tocontact pad 240 for pad-out through at least contact 244 and peripheralcontact 248. Peripheral contacts 246, 247, and 248 each can include oneor more conductive layers, such as a metal layer (e.g., W, Co, Cu, orAl) or a silicide layer surrounded by an adhesive layer (e.g., TiN).

As shown in FIG. 2 , 3D memory device 200 also includes a variety oflocal contacts (also known as “Cl”) as part of the interconnectstructure, which are in contact with a structure in memory stack 214directly. In some embodiments, the local contacts include channel localcontacts 250 each below and in contact with the lower end of respectivechannel structure 224. Each channel local contact 250 can beelectrically connected to a bit line contact (not shown) for bit linefan-out. In some embodiments, the local contacts further include wordline local contacts 252 each below and in contact with respectiveconductive layer 216 (including a word line) at the staircase structureof memory stack 214 for word line fan-out. Local contacts, such aschannel local contacts 250 and word line local contacts 252, can beelectrically connected to peripheral circuits 208 of first semiconductorstructure 202 through at least bonding layers 212 and 210. Localcontacts, such as channel local contacts 250 and word line localcontacts 252, each can include one or more conductive layers, such as ametal layer (e.g., W, Co, Cu, or Al) or a silicide layer surrounded byan adhesive layer (e.g., TiN).

FIGS. 3A-3N illustrate a fabrication process for forming an exemplary 3Dmemory device, according to some embodiments of the present disclosure.FIG. 5A illustrates a flowchart of a method 500 for forming an exemplary3D memory device, according to some embodiments of the presentdisclosure. FIG. 5B illustrates a flowchart of another method 501 forforming an exemplary 3D memory device, according to some embodiments ofthe present disclosure. Examples of the 3D memory device depicted inFIGS. 3A-3N, 5A, and 5B include 3D memory device 100 depicted in FIG. 1. FIGS. 3A-3N, 5A, and 5B will be described together. It is understoodthat the operations shown in methods 500 and 501 are not exhaustive andthat other operations can be performed as well before, after, or betweenany of the illustrated operations. Further, some of the operations maybe performed simultaneously, or in a different order than shown in FIGS.5A and 5B.

Referring to FIG. 5A, method 500 starts at operation 502, in which aperipheral circuit is formed on a first substrate. The first substratecan be a silicon substrate. As illustrated in FIG. 3G, a plurality oftransistors are formed on a silicon substrate 350 using a plurality ofprocesses including, but not limited to, photolithography, etching, thinfilm deposition, thermal growth, implantation, chemical mechanicalpolishing (CMP), and any other suitable processes. In some embodiments,doped regions (not shown) are formed in silicon substrate 350 by ionimplantation and/or thermal diffusion, which function, for example, assource regions and/or drain regions of the transistors. In someembodiments, isolation regions (e.g., STIs) are also formed in siliconsubstrate 350 by wet etching and/or dry etching and thin filmdeposition. The transistors can form peripheral circuits 352 on siliconsubstrate 350.

As illustrated in FIG. 3G, a bonding layer 348 is formed aboveperipheral circuits 352. Bonding layer 348 includes bonding contactselectrically connected to peripheral circuits 352. To form bonding layer348, an ILD layer is deposited using one or more thin film depositionprocesses, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or any combinationthereof; the bonding contacts through the ILD layer are formed using wetetching and/or dry etching, e.g., reactive ion etching (RIE), followedby one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof.

A channel structure extending vertically through a memory stack and anN-type doped semiconductor layer can be formed above a second substrate.Method 500 proceeds to operation 504, as illustrated in FIG. 5A, inwhich a sacrificial layer on the second substrate, the N-type dopedsemiconductor layer on the sacrificial layer, and a dielectric stack onthe N-type doped semiconductor layer are subsequently formed. The secondsubstrate can be a silicon substrate. It is understood that as thesecond substrate will be removed from the final product, the secondsubstrate may be part of a dummy wafer, for example, a carriersubstrate, made of any suitable materials, such as glass, sapphire,plastic, silicon, to name a few, to reduce the cost of the secondsubstrate. In some embodiments, the substrate is a carrier substrate,the sacrificial layer includes a dielectric material, the N-type dopedsemiconductor layer includes polysilicon, and the dielectric stackincludes interleaved stack dielectric layers and stack sacrificiallayers. In some embodiments, the stack dielectric layers and stacksacrificial layers are alternatingly deposited on the N-type dopedsemiconductor layer to form the dielectric stack.

As illustrated in FIG. 3A, a sacrificial layer 304 is formed on acarrier substrate 302, and an N-type doped semiconductor layer 306 isformed on sacrificial layer 304. N-type doped semiconductor layer 306can include polysilicon doped with N-type dopant(s), such as P, As, orSb. Sacrificial layer 304 can include any suitable sacrificial materialsthat can be later selectively removed and are different from thematerial of N-type doped semiconductor layer 306. In some embodiments,sacrificial layer 304 includes a dielectric material, such as siliconoxide or silicon nitride. To form sacrificial layer 304, silicon oxideor silicon nitride is deposited on carrier substrate 302 using one ormore thin film deposition processes including, but not limited to, CVD,PVD, ALD, or any combination thereof, according to some embodiments. Insome embodiments, to form N-type doped semiconductor layer 306,polysilicon is deposited on sacrificial layer 304 using one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof, followed by doping the deposited polysiliconwith N-type dopant(s), such as P, As or Sb, using ion implantationand/or thermal diffusion. In some embodiments, to form N-type dopedsemiconductor layer 306, in-situ doping of N-type dopants, such as P,As, or Sb, is performed when depositing polysilicon on sacrificial layer304.

As illustrated in FIG. 3B, a dielectric stack 308 including a pluralitypairs of a first dielectric layer (referred to herein as “stacksacrificial layer” 312) and a second dielectric layer (referred toherein as “stack dielectric layers” 310, together referred to herein as“dielectric layer pairs”) is formed on N-type doped semiconductor layer306. Dielectric stack 308 includes interleaved stack sacrificial layers312 and stack dielectric layers 310, according to some embodiments.Stack dielectric layers 310 and stack sacrificial layers 312 can bealternatively deposited on N-type doped semiconductor layer 306 abovecarrier substrate 302 to form dielectric stack 308. In some embodiments,each stack dielectric layer 310 includes a layer of silicon oxide, andeach stack sacrificial layer 312 includes a layer of silicon nitride.Dielectric stack 308 can be formed by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, or anycombination thereof. As illustrated in FIG. 3B, a staircase structurecan be formed on the edge of dielectric stack 308. The staircasestructure can be formed by performing a plurality of so-called“trim-etch” cycles to the dielectric layer pairs of dielectric stack 308toward carrier substrate 302. Due to the repeated trim-etch cyclesapplied to the dielectric layer pairs of dielectric stack 308,dielectric stack 308 can have one or more tilted edges and a topdielectric layer pair shorter than the bottom one, as shown in FIG. 3B.

Method 500 proceeds to operation 506, as illustrated in FIG. 5A, inwhich a channel structure extending vertically through the dielectricstack and the N-type doped semiconductor layer is formed. In someembodiments, to form the channel structure, a channel hole extendingvertically through the dielectric stack and the N-type dopedsemiconductor layer, stopping at the sacrificial layer, is etched, and amemory film and a semiconductor channel are subsequently deposited alonga sidewall of the channel hole.

As illustrated in FIG. 3B, a channel hole is an opening extendingvertically through dielectric stack 308 and N-type doped semiconductorlayer 306. In some embodiments, a plurality of openings are formed, suchthat each opening becomes the location for growing an individual channelstructure 314 in the later process. In some embodiments, fabricationprocesses for forming the channel hole of channel structure 314 includewet etching and/or dry etching, such as deep RIE (DRIE). Sacrificiallayer 304 can act as an etch stop layer to control the gouging variationamong different channel holes. For example, the etching of channel holesmay be stopped by sacrificial layer 304 without extending further intocarrier substrate 302. That is, the lower end of each channel hole (andcorresponding channel structure 314) is between the top surface andbottom surface of sacrificial layer 304, according to some embodiments.

As illustrated in FIG. 3B, a memory film including a blocking layer 317,a storage layer 316, and a tunneling layer 315, and a semiconductorchannel 318 are subsequently formed in this order along sidewalls andthe bottom surface of the channel hole. In some embodiments, blockinglayer 317, storage layer 316, and tunneling layer 315 are firstdeposited along the sidewalls and bottom surface of the channel hole inthis order using one or more thin film deposition processes, such asALD, CVD, PVD, any other suitable processes, or any combination thereof,to form the memory film. Semiconductor channel 318 then can be formed bydepositing a semiconductor material, such as polysilicon (e.g., undopedpolysilicon), over tunneling layer 315 using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. In some embodiments, a firstsilicon oxide layer, a silicon nitride layer, a second silicon oxidelayer, and a polysilicon layer (a “SONO” structure) are subsequentlydeposited to form blocking layer 317, storage layer 316, and tunnelinglayer 315 of the memory film and semiconductor channel 318.

As illustrated in FIG. 3B, a capping layer is formed in the channel holeand over semiconductor channel 318 to completely or partially fill thechannel hole (e.g., without or with an air gap). The capping layer canbe formed by depositing a dielectric material, such as silicon oxide,using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. A channel plugthen can be formed in the top portion of the channel hole. In someembodiments, parts of the memory film, semiconductor channel 318, andthe capping layer that are on the top surface of dielectric stack 308are removed and planarized by CMP, wet etching, and/or dry etching. Arecess then can be formed in the top portion of the channel hole by wetetching and/or drying etching parts of semiconductor channel 318 and thecapping layer in the top portion of the channel hole. The channel plugthen can be formed by depositing semiconductor materials, such aspolysilicon, into the recess by one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof. Channelstructure 314 is thereby formed through dielectric stack 308 and N-typedoped semiconductor layer 306. Depending on the depth at which theetching of each channel hole stops by sacrificial layer 304, channelstructure 314 may extend further into sacrificial layer 304 or stop atthe interface between sacrificial layer 304 and N-type dopedsemiconductor layer 306. Nevertheless, channel structure 314 may notextend further into carrier substrate 302.

Method 500 proceeds to operation 508, as illustrated in FIG. 5A, inwhich the dielectric stack is replaced with a memory stack, for example,using the so-called “gate replacement” process, such that the channelstructure extends vertically through the memory stack and the N-typedoped semiconductor layer. In some embodiments, to replace thedielectric stack with the memory stack, an opening extending verticallythrough the dielectric stack, stopping at the N-type doped semiconductorlayer, is etched, and the stack sacrificial layers are replaced withstack conductive layers through the opening to form the memory stackincluding interleaved the stack dielectric layers and the stackconductive layers.

As illustrated in FIG. 3C, a slit 320 is an opening that extendsvertically through dielectric stack 308 and stops at N-type dopedsemiconductor layer 306. In some embodiments, fabrication processes forforming slit 320 include wet etching and/or dry etching, such as DRIE. Agate replacement then can be performed through slit 320 to replacedielectric stack 308 with a memory stack 330 (shown in FIG. 3E).

As illustrated in FIG. 3D, lateral recesses 322 are first formed byremoving stack sacrificial layers 312 (shown in FIG. 3C) through slit320. In some embodiments, stack sacrificial layers 312 are removed byapplying etchants through slit 320, creating lateral recesses 322interleaved between stack dielectric layers 310. The etchants caninclude any suitable etchants that etch stack sacrificial layers 312selective to stack dielectric layers 310.

As illustrated in FIG. 3E, stack conductive layers 328 (including gateelectrodes and adhesive layers) are deposited into lateral recesses 322(shown in FIG. 3D) through slit 320. In some embodiments, a gatedielectric layer 332 is deposited into lateral recesses 322 prior tostack conductive layers 328, such that stack conductive layers 328 aredeposited on gate dielectric layer 332. Stack conductive layers 328,such as metal layers, can be deposited using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. In some embodiments, gatedielectric layer 332, such as a high-k dielectric layer, is formed alongthe sidewall and at the bottom of slit 320 as well. Memory stack 330including interleaved stack conductive layers 328 and stack dielectriclayers 310 is thereby formed, replacing dielectric stack 308 (shown inFIG. 3D), according to some embodiments.

Method 500 proceeds to operation 510, as illustrated in FIG. 5A, inwhich an insulating structure extending vertically through the memorystack is formed. In some embodiments, to form the insulating structure,after forming the memory stack, one or more dielectric materials aredeposited into the opening to fill the opening. As illustrated in FIG.3E, an insulating structure 336 extending vertically through memorystack 330 is formed, stopping on the top surface of N-type dopedsemiconductor layer 306. Insulating structure 336 can be formed bydepositing one or more dielectric materials, such as silicon oxide, intoslit 320 to fully or partially fill slit 320 (with or without an airgap) using one or more thin film deposition processes, such as ALD, CVD,PVD, any other suitable processes, or any combination thereof. In someembodiments, insulating structure 336 includes gate dielectric layer 332(e.g., including high-k dielectrics) and a dielectric capping layer 334(e.g., including silicon oxide).

As illustrated in FIG. 3F, after the formation of insulating structure336, local contacts, including channel local contacts 344 and word linelocal contacts 342, and peripheral contacts 338 and 340 are formed. Alocal dielectric layer can be formed on memory stack 330 by depositingdielectric materials, such as silicon oxide or silicon nitride, usingone or more thin film deposition processes, such as CVD, PVD, ALD, orany combination thereof, on top of memory stack 330. Channel localcontacts 344, word line local contacts 342, and peripheral contacts 338and 340 can be formed by etching contact openings through the localdielectric layer (and any other ILD layers) using wet etching and/or dryetching, e.g., RIE, followed by filling the contact openings withconductive materials using one or more thin film deposition processes,such as ALD, CVD, PVD, any other suitable processes, or any combinationthereof.

As illustrated in FIG. 3F, a bonding layer 346 is formed above channellocal contacts 344, word line local contacts 342, and peripheralcontacts 338 and 340. Bonding layer 346 includes bonding contactselectrically connected to channel local contacts 344, word line localcontacts 342, and peripheral contacts 338 and 340. To form bonding layer346, an ILD layer is deposited using one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof, and thebonding contacts are formed through the ILD layer using wet etchingand/or dry etching, e.g., RIE, followed by one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

Method 500 proceeds to operation 512, as illustrated in FIG. 5A, inwhich the first substrate and the second substrate are bonded in aface-to-face manner, such that the memory stack is above the peripheralcircuit. The bonding can include hybrid bonding. As illustrated in FIG.3G, carrier substrate 302 and components formed thereon (e.g., memorystack 330 and channel structures 314 formed therethrough) are flippedupside down. Bonding layer 346 facing down is bonded with bonding layer348 facing up, i.e., in a face-to-face manner, thereby forming a bondinginterface 354 between carrier substrate 302 and silicon substrate 350,according to some embodiments. In some embodiments, a treatment process,e.g., a plasma treatment, a wet treatment, and/or a thermal treatment,is applied to the bonding surfaces prior to the bonding. After thebonding, the bonding contacts in bonding layer 346 and the bondingcontacts in bonding layer 348 are aligned and in contact with oneanother, such that memory stack 330 and channel structures 314 formedtherethrough can be electrically connected to peripheral circuits 352and are above peripheral circuits 352.

Method 500 proceeds to operation 514, as illustrated in FIG. 5A, inwhich the second substrate and the sacrificial layer are removed toexpose an end of the channel structure. The removal can be performedfrom the backside of the second substrate. As illustrated in FIG. 3H,carrier substrate 302 and sacrificial layer 304 (shown in FIG. 3G) areremoved from the backside to expose an upper end of channel structure314. Carrier substrate 302 can be completely removed using CMP,grinding, dry etching, and/or wet etching. In some embodiments, carriersubstrate 302 is peeled off. The removal of carrier substrate 302 can bestopped by sacrificial layer 304 underneath due to the differentmaterials thereof to ensure thickness uniformity. In some embodiments inwhich carrier substrate 302 includes silicon and sacrificial layer 304includes silicon oxide, carrier substrate 302 is removed using CMP,which can be automatically stopped at the interface between carriersubstrate 302 and sacrificial layer 304.

Sacrificial layer 304 then can be selectively removed as well using wetetching with suitable etchants, such as hydrofluoric acid, withoutetching N-type doped semiconductor layer 306 underneath. As describedabove, since channel structure 314 does not extend beyond sacrificiallayer 304 into carrier substrate 302, the removal of carrier substrate302 does not affect channel structure 314. The removal of sacrificiallayer 304 can expose the upper end of channel structure 314. In someembodiments in which channel structure 314 extends into sacrificiallayer 304, the selective etching of sacrificial layer 304 includingsilicon oxide also removes part of blocking layer 317 including siliconoxide above the top surface of N-type doped semiconductor layer 306, butstorage layer 316 including silicon nitride and other layers surroundedby storage layer 316 (e.g., tunneling layer 315) remain intact.

Method 500 proceeds to operation 516, as illustrated in FIG. 5A, inwhich part of the channel structure abutting the N-type dopedsemiconductor layer is replaced with a semiconductor plug. In someembodiments, to replace the part of the channel structure abutting theN-type doped semiconductor layer with the semiconductor plug, part ofthe memory film abutting the N-type doped semiconductor layer is removedto form a recess surrounding part of the semiconductor channel, the partof the semiconductor channel is doped, and polysilicon is deposited intothe recess to form the semiconductor plug surrounding and in contactwith the part of the doped semiconductor channel.

As illustrated in FIG. 3I, part of storage layer 316 (shown in FIG. 3H)abutting N-type doped semiconductor layer 306 is removed. In someembodiments, storage layer 316 including silicon nitride is selectivelyremoved using wet etching with suitable etchants, such as phosphoricacid, without etching N-type doped semiconductor layer 306 includingpolysilicon. The etching of storage layer 316 can be controlled bycontrolling the etching time and/or etching rate, such that the etchingdoes not continue to affect the rest of storage layer 316 surrounded bymemory stack 330.

As illustrated in FIG. 3J, parts of blocking layer 317 and tunnelinglayer 315 abutting N-type doped semiconductor layer 306 are removed toform a recess 357 surrounding the top portion of semiconductor channel318 abutting N-type doped semiconductor layer 306. In some embodiments,blocking layer 317 and tunneling layer 315 including silicon oxide areselectively removed using wet etching with suitable etchants, such ashydrofluoric acid, without etching N-type doped semiconductor layer 306and semiconductor channel 318 including polysilicon. The etching ofblocking layer 317 and tunneling layer 315 can be controlled bycontrolling the etching time and/or etching rate, such that the etchingdoes not continue to affect the rest of blocking layer 317 and tunnelinglayer 315 surrounded by memory stack 330. As a result, the top portionof the memory film (including blocking layer 317, storage layer 316, andtunneling layer 315) of channel structure 314 abutting N-type dopedsemiconductor layer 306 is removed to form recess 357, exposing the topportion of semiconductor channel 318, according to some embodiments. Insome embodiments, the top portion of semiconductor channel 318 exposedby recess 357 is doped to increase its conductivity. For example, atilted ion implantation process may be performed to dope the top portionof semiconductor channel 318 (e.g., including polysilicon) exposed byrecess 357 with any suitable dopants to a desired doping concentration.

As illustrated in FIG. 3K, a semiconductor plug 359 is formed in recess357 (shown in FIG. 3J), surrounding and in contact with the doped topportion of semiconductor channel 318. As a result, the top portion ofchannel structure 314 (shown in FIG. 3H) abutting N-type dopedsemiconductor layer 306 is thereby replaced with semiconductor plug 359,according to some embodiments. In some embodiments, to formsemiconductor plug 359, polysilicon is deposited into recess 357 usingone or more thin film deposition processes, such as ALD, CVD, PVD, anyother suitable processes, or any combination thereof to fill recess 357,followed by a CMP process to remove any excess polysilicon above the topsurface of N-type doped semiconductor layer 306. In some embodiments,in-situ doping of N-type dopants, such as P, As, or Sb, is performedwhen depositing polysilicon into recess 357 to dope semiconductor plug359. As semiconductor plug 359 and N-type doped semiconductor layer 306may include the same material, such as polysilicon, and have the samethickness (after the CMP process), semiconductor plug 359 may be viewedas part of N-type doped semiconductor layer 306. Nevertheless, assemiconductor plug 359 is formed in a later process after the formationof the rest of N-type doped semiconductor layer 306 (e.g., shown in FIG.3A), regardless whether semiconductor plug 359 is in-situ doped, thedoping concentration of semiconductor plug 359 is different from thedoping concentration of the rest of N-type doped semiconductor layer306, according to some embodiments.

As described above, semiconductor plugs 359 in N-type dopedsemiconductor layer 306 can act as the sidewall SEGs of channelstructures 314. Different from known methods that form the sidewall SEGsby etching and deposition processes through slit 320 (e.g., shown inFIG. 3D) extending all the way through dielectric stack 308 with highaspect ratio, semiconductor plugs 359 can be formed from the oppositeside of dielectric stack 308/memory stack 330 once carrier substrate 302is removed, which is not affected by the level of dielectric stack308/memory stack 330 and the aspect ratio of slit 320. By avoiding theissues introduced by the high aspect ratio of slit 320, the fabricationcomplexity and cost can be reduced, and the yield can be increased.Moreover, the vertical scalability (e.g., the increasing level ofdielectric stack 308/memory stack 330) can be improved as well.

Method 500 proceeds to operation 518, as illustrated in FIG. 5A, inwhich a source contact is formed above the memory stack and in contactwith the N-type doped semiconductor layer. As illustrated in FIG. 3L,one or more ILD layers 356 are formed on N-type doped semiconductorlayer 306. ILD layers 356 can be formed by depositing dielectricmaterials on the top surface of N-type doped semiconductor layer 306using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. A sourcecontact opening 358 can be formed through ILD layers 356 into N-typedoped semiconductor layer 306. In some embodiments, source contactopening 358 is formed using wet etching and/or dry etching, such as RIE.In some embodiments, source contact opening 358 extends further into thetop portion of N-type doped semiconductor layer 306. The etching processthrough ILD layers 356 may continue to etch part of N-type dopedsemiconductor layer 306. In some embodiments, a separate etching processis used to etch part of N-type doped semiconductor layer 306 afteretching through ILD layers 356.

As illustrated in FIG. 3M, a source contact 364 is formed in sourcecontact opening 358 (shown in FIG. 3L) at the backside of N-type dopedsemiconductor layer 306. Source contact 364 is above memory stack 330and in contact with N-type doped semiconductor layer 306, according tosome embodiments. In some embodiments, one or more conductive materialsare deposited into source contact opening 358 using one or more thinfilm deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof, to fill source contact opening358 with an adhesive layer (e.g., TiN) and a conductor layer (e.g., W).A planarization process, such as CMP, can then be performed to removethe excess conductive materials, such that the top surface of sourcecontact 364 is flush with the top surface of ILD layers 356.

Method 500 proceeds to operation 520, as illustrated in FIG. 5A, inwhich an interconnect layer is formed above and in contact with thesource contact. In some embodiments, a contact is formed through theN-type doped semiconductor layer and in contact with the interconnectlayer, such that the N-type doped semiconductor layer is electricallyconnected to the contact through the source contact and the interconnectlayer.

As illustrated in FIG. 3N, a redistribution layer 370 is formed aboveand in contact with source contact 364. In some embodiments,redistribution layer 370 is formed by depositing a conductive material,such as Al, on the top surfaces of ILD layers 356 and source contact 364using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. A passivationlayer 372 can be formed on redistribution layer 370. In someembodiments, passivation layer 372 is formed by depositing a dielectricmaterial, such as silicon nitride, using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. An interconnect layer 376including ILD layers 356, redistribution layer 370, and passivationlayer 372 is thereby formed, according to some embodiments.

As illustrated in FIG. 3L, contact openings 360 and 361 each extendingthrough ILD layers 356 and N-type doped semiconductor layer 306 areformed. In some embodiments, contact openings 360 and 361 are formedusing wet etching and/or dry etching, such as RIE, through ILD layers356 and N-type doped semiconductor layer 306. In some embodiments,contact openings 360 and 361 are patterned using lithography to bealigned with peripheral contacts 338 and 340, respectively. The etchingof contact openings 360 and 361 can stop at the upper ends of peripheralcontacts 338 and 340 to expose peripheral contacts 338 and 340. Asillustrated in FIG. 3L, a spacer 362 is formed along the sidewalls ofcontact openings 360 and 361 to electrically separate N-type dopedsemiconductor layer 306 using one or more thin film depositionprocesses, such as ALD, CVD, PVD, any other suitable processes, or anycombination thereof. In some embodiments, the etching of source contactopening 358 is performed after the formation of spacer 362, such thatspacer 362 is not formed along the sidewall of source contact opening358 to increase the contact area between source contact 364 and N-typedoped semiconductor layer 306.

As illustrated in FIG. 3M, contacts 366 and 368 are formed in contactopenings 360 and 361, respectively (shown in FIG. 3L) at the backside ofN-type doped semiconductor layer 306. Contacts 366 and 368 extendvertically through ILD layers 356 and N-type doped semiconductor layer306, according to some embodiments. Contacts 366 and 368 and sourcecontact 364 can be formed using the same deposition process to reducethe number of deposition processes. In some embodiments, one or moreconductive materials are deposited into contact openings 360 and 361using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof, to fillcontact openings 360 and 361 with an adhesive layer (e.g., TiN) and aconductor layer (e.g., W). A planarization process, such as ClVIP, canthen be performed to remove the excess conductive materials, such thatthe top surfaces of contacts 366 and 368 (and the top surface of sourcecontact 364) are flush with the top surface of ILD layers 356. In someembodiments, as contact openings 360 and 361 are aligned with peripheralcontacts 338 and 340, respectively, contacts 366 and 368 are above andin contact with peripheral contacts 338 and 340, respectively, as well.

As illustrated in FIG. 3N, redistribution layer 370 is also formed aboveand in contact with contact 366. As a result, N-type doped semiconductorlayer 306 can be electrically connected to peripheral contact 338through source contact 364, redistribution layer 370 of interconnectlayer 376, and contact 366. In some embodiments, N-type dopedsemiconductor layer 306 is electrically connected to peripheral circuits352 through source contact 364, interconnect layer 376, contact 366,peripheral contact 338, and bonding layers 346 and 348.

As illustrated in FIG. 3N, a contact pad 374 is formed above and incontact with contact 368. In some embodiments, part of passivation layer372 covering contact 368 is removed by wet etching and/or dry etching toexpose part of redistribution layer 370 underneath to form contact pad374. As a result, contact pad 374 for pad-out can be electricallyconnected to peripheral circuits 352 through contact 368, peripheralcontact 340, and bonding layers 346 and 348.

It is understood that the second substrate, sacrificial layer, andN-type doped semiconductor layer described above in method 500 may bereplaced by an SOI wafer, which includes a handling layer, a buriedoxide layer (also known as a “BOX” layer), and a device layer asdescribed below with respect to method 501. The detail of similaroperations between methods 500 and 501 may not be repeated for ease ofdescription. Referring to FIG. 5B, method 501 starts at operation 502,in which a peripheral circuit is formed on a first substrate. The firstsubstrate can be a silicon substrate.

Method 501 proceeds to operation 503, as illustrated in FIG. 5B, inwhich a device layer of an SOI wafer is doped with an N-type dopant. TheSOI wafer can include a handling layer, a buried oxide layer, and adevice layer. In some embodiments, the buried oxide layer includessilicon oxide, and the device layer includes single crystalline silicon.As illustrated in FIG. 3A, an SOI wafer 301 includes a handling layer302 (corresponding to carrier substrate 302 above in describing method500), a buried oxide layer 304 (corresponding to sacrificial layer 304),and a device layer 306 (corresponding to N-type doped semiconductorlayer 306). Device layer 306 can be doped with N-type dopant(s), such asP, As, or Sb, using ion implantation and/or thermal diffusion to becomean N-type doped device layer 306. It is understood that the abovedescriptions related to carrier substrate 302, sacrificial layer 304,and N-type doped semiconductor layer 306 can be similarly applied tohandling layer 302, buried oxide layer 304, and doped device layer 306of SOI wafer 301, respectively, to better understand method 501 belowand thus, are not repeated for ease of description.

Method 501 proceeds to operation 505, as illustrated in FIG. 5B, inwhich a dielectric stack is formed on the doped device layer of the SOIwafer. The dielectric stack can include interleaved stack dielectriclayers and stack sacrificial layers. Method 501 proceeds to operation507, as illustrated in FIG. 5B, in which a channel structure extendingvertically through the dielectric stack and the doped device layer isformed. In some embodiments, to form the channel structure, a channelhole extending vertically through the dielectric stack and the dopeddevice layer, stopping at the buried oxide layer, is formed, and amemory film and a semiconductor channel are subsequently deposited alonga sidewall of the channel hole. Method 501 proceeds to operation 508, asillustrated in FIG. 5B, in which the dielectric stack is replaced with amemory stack, such that the channel structure extends vertically throughthe memory stack and the doped device layer. In some embodiments, toreplace the dielectric stack with the memory stack, an opening extendingvertically through the dielectric stack is etched, stopping at the dopeddevice layer, and the stack sacrificial layers are replaced with stackconductive layers through the opening to form the memory stack includinginterleaved the stack dielectric layers and the stack conductive layers.Method 501 proceeds to operation 510, as illustrated in FIG. 5B, inwhich an insulating structure extending vertically through the memorystack is formed. In some embodiments, to form the insulating structure,after forming the memory stack, one or more dielectric materials aredeposited into the opening to fill the opening.

Method 501 proceeds to operation 513, as illustrated in FIG. 5B, inwhich the first substrate and the SOI wafer are bonded in a face-to-facemanner, such that the memory stack is above the peripheral circuit. Thebonding can include hybrid bonding. Method 501 proceeds to operation515, as illustrated in FIG. 5B, in which the handle layer and the buriedoxide layer of the SOI wafer are removed to expose an end of the channelstructure. Method 501 proceeds to operation 517, as illustrated in FIG.5B, in which part of the channel structure abutting the doped devicelayer is replaced with a semiconductor plug. In some embodiments, toreplace the part of the channel structure abutting the doped devicelayer with the semiconductor plug, part of the memory film abutting thedoped device layer is etched to form a recess surrounding part of thesemiconductor channel, the part of the semiconductor channel is doped,and polysilicon is deposited into the recess to form the semiconductorplug surrounding and in contact with the part of the doped semiconductorchannel.

Method 501 proceeds to operation 519, as illustrated in FIG. 5B, inwhich a source contact above the memory stack and in contact with thedoped device layer is formed. Method 501 proceeds to operation 520, asillustrated in FIG. 5B, in which an interconnect layer above and incontact with the source contact is formed. In some embodiments, acontact is formed through the doped device layer and in contact with theinterconnect layer, such that the doped device layer is electricallyconnected to the contact through the source contact and the interconnectlayer.

FIGS. 4A-4O illustrate a fabrication process for forming anotherexemplary 3D memory device, according to some embodiments of the presentdisclosure. FIG. 6A illustrates a flowchart of a method 600 for forminganother exemplary 3D memory device, according to some embodiments of thepresent disclosure. FIG. 6B illustrates a flowchart of another method601 for forming another exemplary 3D memory device, according to someembodiments of the present disclosure. Examples of the 3D memory devicedepicted in FIGS. 4A-4O, 6A, and 6B include 3D memory device 200depicted in FIG. 2 . FIGS. 4A-4O, 6A, and 6B will be described together.It is understood that the operations shown in methods 600 and 601 arenot exhaustive and that other operations can be performed as wellbefore, after, or between any of the illustrated operations. Further,some of the operations may be performed simultaneously, or in adifferent order than shown in FIGS. 6A and 6B.

Referring to FIG. 6A, method 600 starts at operation 602, in which aperipheral circuit is formed on a first substrate. The first substratecan be a silicon substrate. As illustrated in FIG. 4G, a plurality oftransistors are formed on a silicon substrate 450 using a plurality ofprocesses including, but not limited to, photolithography, etching, thinfilm deposition, thermal growth, implantation, CMP, and any othersuitable processes. In some embodiments, doped regions (not shown) areformed in silicon substrate 450 by ion implantation and/or thermaldiffusion, which function, for example, as source regions and/or drainregions of the transistors. In some embodiments, isolation regions(e.g., STIs) are also formed in silicon substrate 450 by wet etchingand/or dry etching and thin film deposition. The transistors can formperipheral circuits 452 on silicon substrate 450.

As illustrated in FIG. 4G, a bonding layer 448 is formed aboveperipheral circuits 452. Bonding layer 448 includes bonding contactselectrically connected to peripheral circuits 452. To form bonding layer448, an ILD layer is deposited using one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof; thebonding contacts through the ILD layer are formed using wet etchingand/or dry etching, e.g., RIE, followed by one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

A channel structure extending vertically through a memory stack and aP-type doped semiconductor layer having an N-well can be formed above asecond substrate. Method 600 proceeds to operation 604, as illustratedin FIG. 6A, in which a sacrificial layer on the second substrate, theP-type doped semiconductor layer having the N-well on the sacrificiallayer, and a dielectric stack on the P-type doped semiconductor layerare subsequently formed. The second substrate can be a siliconsubstrate. It is understood that as the second substrate will be removedfrom the final product, the second substrate may be part of a dummywafer, for example, a carrier substrate, made of any suitable materials,such as glass, sapphire, plastic, silicon, to name a few, to reduce thecost of the second substrate. In some embodiments, the substrate is acarrier substrate, the sacrificial layer includes a dielectric material,the P-type doped semiconductor layer includes polysilicon, and thedielectric stack includes interleaved stack dielectric layers and stacksacrificial layers. In some embodiments, the stack dielectric layers andstack sacrificial layers are alternatingly deposited on the P-type dopedsemiconductor layer to form the dielectric stack. In some embodiments,prior to forming the dielectric stack, part of the P-type dopedsemiconductor layer is doped with an N-type dopant to form the N-well.

As illustrated in FIG. 4A, a sacrificial layer 404 is formed on acarrier substrate 402, and a P-type doped semiconductor layer 406 isformed on sacrificial layer 404. P-type doped semiconductor layer 406can include polysilicon doped with P-type dopant(s), such as B, Ga, orAl. Sacrificial layer 404 can include any suitable sacrificial materialsthat can be later selectively removed and are different from thematerial of P-type doped semiconductor layer 406. In some embodiments,sacrificial layer 404 includes a dielectric material, such as siliconoxide or silicon nitride. To form sacrificial layer 404, silicon oxideor silicon nitride is deposited on carrier substrate 402 using one ormore thin film deposition processes including, but not limited to, CVD,PVD, ALD, or any combination thereof, according to some embodiments. Insome embodiments, to form P-type doped semiconductor layer 406,polysilicon is deposited on sacrificial layer 404 using one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof, followed by doping the deposited polysiliconwith P-type dopant(s), such as B, Ga, or Al, using ion implantationand/or thermal diffusion. In some embodiments, to form P-type dopedsemiconductor layer 406, in-situ doping of P-type dopants, such as B,Ga, or Al, is performed when depositing polysilicon on sacrificial layer404.

As illustrated in FIG. 4A, part of P-type doped semiconductor layer 406is doped with N-type dopant(s), such as P, As, or Sb, to form an N-well407 in P-type doped semiconductor layer 406. In some embodiments, N-well407 is formed using ion implantation and/or thermal diffusion. The ionimplantation and/or thermal diffusion processes can be controlled tocontrol the thickness of N-well 407, either through the entire thicknessof P-type doped semiconductor layer 406 or part thereof.

As illustrated in FIG. 4B, a dielectric stack 408 including a pluralitypairs of a first dielectric layer (referred to herein as “stacksacrificial layer” 412) and a second dielectric layer (referred toherein as “stack dielectric layers” 410, together referred to herein as“dielectric layer pairs”) is formed on P-type doped semiconductor layer406. Dielectric stack 408 includes interleaved stack sacrificial layers412 and stack dielectric layers 410, according to some embodiments.Stack dielectric layers 410 and stack sacrificial layers 412 can bealternatively deposited on P-type doped semiconductor layer 406 abovecarrier substrate 402 to form dielectric stack 408. In some embodiments,each stack dielectric layer 410 includes a layer of silicon oxide, andeach stack sacrificial layer 412 includes a layer of silicon nitride.Dielectric stack 408 can be formed by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, or anycombination thereof. As illustrated in FIG. 4B, a staircase structurecan be formed on the edge of dielectric stack 408. The staircasestructure can be formed by performing a plurality of so-called“trim-etch” cycles to the dielectric layer pairs of dielectric stack 408toward carrier substrate 402. Due to the repeated trim-etch cyclesapplied to the dielectric layer pairs of dielectric stack 408,dielectric stack 408 can have one or more tilted edges and a topdielectric layer pair shorter than the bottom one, as shown in FIG. 4B.

Method 600 proceeds to operation 606, as illustrated in FIG. 6A, inwhich a channel structure extending vertically through the dielectricstack and the P-type doped semiconductor layer is formed. In someembodiments, to form the channel structure, a channel hole extendingvertically through the dielectric stack and the P-type dopedsemiconductor layer, stopping at the sacrificial layer, is etched, and amemory film and a semiconductor channel are subsequently deposited alonga sidewall of the channel hole.

As illustrated in FIG. 4B, a channel hole is an opening extendingvertically through dielectric stack 408 and P-type doped semiconductorlayer 406. In some embodiments, a plurality of openings are formed, suchthat each opening becomes the location for growing an individual channelstructure 414 in the later process. In some embodiments, fabricationprocesses for forming the channel hole of channel structure 414 includewet etching and/or dry etching, such as DRIE. Sacrificial layer 404 canact as an etch stop layer to control the gouging variation amongdifferent channel holes. For example, the etching of channel holes maybe stopped by sacrificial layer 404 without extending further intocarrier substrate 402. That is, the lower end of each channel hole (andcorresponding channel structure 414) is between the top surface andbottom surface of sacrificial layer 404, according to some embodiments.

As illustrated in FIG. 4B, a memory film including a blocking layer 417,a storage layer 416, and a tunneling layer 415, and a semiconductorchannel 418 are subsequently formed in this order along sidewalls andthe bottom surface of the channel hole. In some embodiments, blockinglayer 417, storage layer 416, and tunneling layer 415 are firstdeposited along the sidewalls and bottom surface of the channel hole inthis order using one or more thin film deposition processes, such asALD, CVD, PVD, any other suitable processes, or any combination thereof,to form the memory film. Semiconductor channel 418 then can be formed bydepositing a semiconductor material, such as polysilicon (e.g., undopedpolysilicon), over tunneling layer 415 using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. In some embodiments, a firstsilicon oxide layer, a silicon nitride layer, a second silicon oxidelayer, and a polysilicon layer (a “SONO” structure) are subsequentlydeposited to form blocking layer 417, storage layer 416, and tunnelinglayer 415 of the memory film and semiconductor channel 418.

As illustrated in FIG. 4B, a capping layer is formed in the channel holeand over semiconductor channel 418 to completely or partially fill thechannel hole (e.g., without or with an air gap). The capping layer canbe formed by depositing a dielectric material, such as silicon oxide,using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. A channel plugthen can be formed in the top portion of the channel hole. In someembodiments, parts of the memory film, semiconductor channel 418, andthe capping layer that are on the top surface of dielectric stack 408are removed and planarized by CMP, wet etching, and/or dry etching. Arecess then can be formed in the top portion of the channel hole by wetetching and/or drying etching parts of semiconductor channel 418 and thecapping layer in the top portion of the channel hole. The channel plugthen can be formed by depositing semiconductor materials, such aspolysilicon, into the recess by one or more thin film depositionprocesses, such as CVD, PVD, ALD, or any combination thereof. Channelstructure 414 is thereby formed through dielectric stack 408 and P-typedoped semiconductor layer 406. Depending on the depth at which theetching of each channel hole stops by sacrificial layer 404, channelstructure 414 may extend further into sacrificial layer 404 or stop atthe interface between sacrificial layer 404 and P-type dopedsemiconductor layer 406. Nevertheless, channel structure 414 may notextend further into carrier substrate 402.

Method 600 proceeds to operation 608, as illustrated in FIG. 6A, inwhich the dielectric stack is replaced with a memory stack, for example,using the so-called “gate replacement” process, such that the channelstructure extends vertically through the memory stack and the P-typedoped semiconductor layer. In some embodiments, to replace thedielectric stack with the memory stack, an opening extending verticallythrough the dielectric stack, stopping at the P-type doped semiconductorlayer, is etched, and the stack sacrificial layers are replaced withstack conductive layers through the opening to form the memory stackincluding interleaved the stack dielectric layers and the stackconductive layers.

As illustrated in FIG. 4C, a slit 420 is an opening that extendsvertically through dielectric stack 408 and stops at P-type dopedsemiconductor layer 406. In some embodiments, fabrication processes forforming slit 420 include wet etching and/or dry etching, such as DRIE.Although slit 420 is laterally aligned with N-well 407 as shown in FIG.4C, it is understood that slit 420 may not be laterally aligned withN-well 407 in other examples. A gate replacement then can be performedthrough slit 420 to replace dielectric stack 408 with a memory stack 430(shown in FIG. 4E).

As illustrated in FIG. 4D, lateral recesses 422 are first formed byremoving stack sacrificial layers 412 (shown in FIG. 4C) through slit420. In some embodiments, stack sacrificial layers 412 are removed byapplying etchants through slit 420, creating lateral recesses 422interleaved between stack dielectric layers 410. The etchants caninclude any suitable etchants that etch stack sacrificial layers 412selective to stack dielectric layers 410.

As illustrated in FIG. 4E, stack conductive layers 428 (including gateelectrodes and adhesive layers) are deposited into lateral recesses 422(shown in FIG. 4D) through slit 420. In some embodiments, a gatedielectric layer 432 is deposited into lateral recesses 422 prior tostack conductive layers 428, such that stack conductive layers 428 aredeposited on gate dielectric layer 432. Stack conductive layers 428,such as metal layers, can be deposited using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. In some embodiments, gatedielectric layer 432, such as a high-k dielectric layer, is formed alongthe sidewall and at the bottom of slit 420 as well. Memory stack 430including interleaved stack conductive layers 428 and stack dielectriclayers 410 is thereby formed, replacing dielectric stack 408 (shown inFIG. 4D), according to some embodiments.

Method 600 proceeds to operation 610, as illustrated in FIG. 6A, inwhich an insulating structure extending vertically through the memorystack is formed. In some embodiments, to form the insulating structure,after forming the memory stack, one or more dielectric materials aredeposited into the opening to fill the opening. As illustrated in FIG.4E, an insulating structure 436 extending vertically through memorystack 430 is formed, stopping on the top surface of P-type dopedsemiconductor layer 406. Insulating structure 436 can be formed bydepositing one or more dielectric materials, such as silicon oxide, intoslit 420 to fully or partially fill slit 420 (with or without an airgap) using one or more thin film deposition processes, such as ALD, CVD,PVD, any other suitable processes, or any combination thereof. In someembodiments, insulating structure 436 includes gate dielectric layer 432(e.g., including high-k dielectrics) and a dielectric capping layer 434(e.g., including silicon oxide).

As illustrated in FIG. 4F, after the formation of insulating structure436, local contacts, including channel local contacts 444 and word linelocal contacts 442, and peripheral contacts 438, 439, and 440 areformed. A local dielectric layer can be formed on memory stack 430 bydepositing dielectric materials, such as silicon oxide or siliconnitride, using one or more thin film deposition processes, such as CVD,PVD, ALD, or any combination thereof, on top of memory stack 430.Channel local contacts 444, word line local contacts 442, and peripheralcontacts 438, 439, and 440 can be formed by etching contact openingsthrough the local dielectric layer (and any other ILD layers) using wetetching and/or dry etching, e.g., RIE, followed by filling the contactopenings with conductive materials using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

As illustrated in FIG. 4F, a bonding layer 446 is formed above channellocal contacts 444, word line local contacts 442, and peripheralcontacts 438, 439, and 440. Bonding layer 446 includes bonding contactselectrically connected to channel local contacts 444, word line localcontacts 442, and peripheral contacts 438, 439, and 440. To form bondinglayer 446, an ILD layer is deposited using one or more thin filmdeposition processes, such as CVD, PVD, ALD, or any combination thereof,and the bonding contacts are formed through the ILD layer using wetetching and/or dry etching, e.g., RIE, followed by one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

Method 600 proceeds to operation 612, as illustrated in FIG. 6A, inwhich the first substrate and the second substrate are bonded in aface-to-face manner, such that the memory stack is above the peripheralcircuit. The bonding can include hybrid bonding. As illustrated in FIG.4G, carrier substrate 402 and components formed thereon (e.g., memorystack 430 and channel structures 414 formed therethrough) are flippedupside down. Bonding layer 446 facing down is bonded with bonding layer448 facing up, i.e., in a face-to-face manner, thereby forming a bondinginterface 454 between carrier substrate 402 and silicon substrate 450,according to some embodiments. In some embodiments, a treatment process,e.g., a plasma treatment, a wet treatment, and/or a thermal treatment,is applied to the bonding surfaces prior to the bonding. After thebonding, the bonding contacts in bonding layer 446 and the bondingcontacts in bonding layer 448 are aligned and in contact with oneanother, such that memory stack 430 and channel structures 414 formedtherethrough can be electrically connected to peripheral circuits 452and are above peripheral circuits 452.

Method 600 proceeds to operation 614, as illustrated in FIG. 6A, inwhich the second substrate and the sacrificial layer are removed toexpose an end of the channel structure. The removal can be performedfrom the backside of the second substrate. As illustrated in FIG. 4H,carrier substrate 402 and sacrificial layer 404 (shown in FIG. 4G) areremoved from the backside to expose an upper end of channel structure414. Carrier substrate 402 can be completely removed using CMP,grinding, dry etching, and/or wet etching. In some embodiments, carriersubstrate 402 is peeled off. The removal of carrier substrate 402 can bestopped by sacrificial layer 404 underneath due to the differentmaterials thereof to ensure thickness uniformity. In some embodiments inwhich carrier substrate 402 includes silicon and sacrificial layer 304includes silicon oxide, carrier substrate 402 is removed using CMP,which can be automatically stopped at the interface between carriersubstrate 402 and sacrificial layer 404.

Sacrificial layer 404 then can be selectively removed as well using wetetching with suitable etchants, such as hydrofluoric acid, withoutetching P-type doped semiconductor layer 406 underneath. As describedabove, since channel structure 414 does not extend beyond sacrificiallayer 404 into carrier substrate 402, the removal of carrier substrate402 does not affect channel structure 414. The removal of sacrificiallayer 404 can expose the upper end of channel structure 414. In someembodiments in which channel structure 414 extends into sacrificiallayer 404, the selective etching of sacrificial layer 404 includingsilicon oxide also removes part of blocking layer 417 including siliconoxide above the top surface of P-type doped semiconductor layer 406, butstorage layer 416 including silicon nitride and other layers surroundedby storage layer 416 (e.g., tunneling layer 415) remain intact.

Method 600 proceeds to operation 616, as illustrated in FIG. 6A, inwhich part of the channel structure abutting the P-type dopedsemiconductor layer is replaced with a semiconductor plug. In someembodiments, to replace the part of the channel structure abutting theP-type doped semiconductor layer with the semiconductor plug, part ofthe memory film abutting the P-type doped semiconductor layer is removedto form a recess surrounding part of the semiconductor channel, the partof the semiconductor channel is doped, and polysilicon is deposited intothe recess to form the semiconductor plug surrounding and in contactwith the part of the doped semiconductor channel.

As illustrated in FIG. 4I, part of storage layer 416 (shown in FIG. 4H)abutting P-type doped semiconductor layer 406 is removed. In someembodiments, storage layer 416 including silicon nitride is selectivelyremoved using wet etching with suitable etchants, such as phosphoricacid, without etching P-type doped semiconductor layer 406 includingpolysilicon. The etching of storage layer 416 can be controlled bycontrolling the etching time and/or etching rate, such that the etchingdoes not continue to affect the rest of storage layer 416 surrounded bymemory stack 430.

As illustrated in FIG. 4J, parts of blocking layer 417 and tunnelinglayer 415 abutting P-type doped semiconductor layer 406 are removed toform a recess 457 surrounding the top portion of semiconductor channel418 abutting P-type doped semiconductor layer 406. In some embodiments,blocking layer 417 and tunneling layer 415 including silicon oxide areselectively removed using wet etching with suitable etchants, such ashydrofluoric acid, without etching P-type doped semiconductor layer 406and semiconductor channel 418 including polysilicon. The etching ofblocking layer 417 and tunneling layer 415 can be controlled bycontrolling the etching time and/or etching rate, such that the etchingdoes not continue to affect the rest of blocking layer 417 and tunnelinglayer 415 surrounded by memory stack 430. As a result, the top portionof the memory film (including blocking layer 417, storage layer 416, andtunneling layer 415) of channel structure 414 abutting P-type dopedsemiconductor layer 406 is removed to form recess 457, exposing the topportion of semiconductor channel 418, according to some embodiments. Insome embodiments, the top portion of semiconductor channel 418 exposedby recess 457 is doped to increase its conductivity. For example, atilted ion implantation process may be performed to dope the top portionof semiconductor channel 418 (e.g., including polysilicon) exposed byrecess 457 with any suitable dopants to a desired doping concentration.

As illustrated in FIG. 4K, a semiconductor plug 459 is formed in recess457 (shown in FIG. 4J), surrounding and in contact with the doped topportion of semiconductor channel 418. As a result, the top portion ofchannel structure 414 (shown in FIG. 4H) abutting P-type dopedsemiconductor layer 406 is thereby replaced with semiconductor plug 459,according to some embodiments. In some embodiments, to formsemiconductor plug 459, polysilicon is deposited into recess 457 usingone or more thin film deposition processes, such as ALD, CVD, PVD, anyother suitable processes, or any combination thereof to fill recess 457,followed by a CMP process to remove excess polysilicon above the topsurface of P-type doped semiconductor layer 406. In some embodiments,in-situ doping of P-type dopants, such as B, Ga, or Al, is performedwhen depositing polysilicon into recess 457 to dope semiconductor plug459. As semiconductor plug 459 and P-type doped semiconductor layer 406may include the same material, such as polysilicon, and have the samethickness (after the CMP process), semiconductor plug 459 may be viewedas part of P-type doped semiconductor layer 406. Nevertheless, assemiconductor plug 459 is formed in a later process after the formationof the rest of P-type doped semiconductor layer 406 (e.g., shown in FIG.4A), regardless whether semiconductor plug 459 is in-situ doped, thedoping concentration of semiconductor plug 459 is different from thedoping concentration of the rest of P-type doped semiconductor layer406, according to some embodiments.

As described above, semiconductor plugs 459 in P-type dopedsemiconductor layer 406 can act as the sidewall SEGs of channelstructures 414. Different from known methods that form the sidewall SEGsby etching and deposition processes through slit 420 (e.g., shown inFIG. 4D) extending all the way through dielectric stack 408 with highaspect ratio, semiconductor plugs 459 can be formed from the oppositeside of dielectric stack 408/memory stack 430 once carrier substrate 402is removed, which is not affected by the level of dielectric stack408/memory stack 430 and the aspect ratio of slit 420. By avoiding theissues introduced by the high aspect ratio of slit 420, the fabricationcomplexity and cost can be reduced, and the yield can be increased.Moreover, the vertical scalability (e.g., the increasing level ofdielectric stack 408/memory stack 430) can be improved as well.

Method 600 proceeds to operation 618, as illustrated in FIG. 6A, inwhich a first source contact is formed above the memory stack and incontact with the P-type doped semiconductor layer, and a second sourcecontact is formed above the memory stack and in contact with the N-well.As illustrated in FIG. 4L, one or more ILD layers 456 are formed onP-type doped semiconductor layer 406. ILD layers 456 can be formed bydepositing dielectric materials on the top surface of P-type dopedsemiconductor layer 406 using one or more thin film depositionprocesses, such as ALD, CVD, PVD, any other suitable processes, or anycombination thereof.

As illustrated in FIG. 4M, a source contact opening 458 can be formedthrough ILD layers 456 into P-type doped semiconductor layer 406. Insome embodiments, source contact opening 458 is formed using wet etchingand/or dry etching, such as RIE. In some embodiments, source contactopening 458 extends further into the top portion of P-type dopedsemiconductor layer 406. The etching process through ILD layers 456 maycontinue to etch part of P-type doped semiconductor layer 406. In someembodiments, a separate etching process is used to etch part of P-typedoped semiconductor layer 406 after etching through ILD layers 456.

As illustrated in FIG. 4M, a source contact opening 465 can be formedthrough ILD layers 456 into N-well 407. In some embodiments, sourcecontact opening 465 is formed using wet etching and/or dry etching, suchas RIE. In some embodiments, source contact opening 465 extends furtherinto the top portion of N-well 407. The etching process through ILDlayers 456 may continue to etch part of N-well 407. In some embodiments,a separate etching process is used to etch part of N-well 407 afteretching through ILD layers 456. The etching of source contact opening458 can be performed after the etching of source contact opening 465 orvice versa. It is understood that in some examples, source contactopenings 458 and 465 may be etched by the same etching process to reducethe number of etching processes.

As illustrated in FIG. 4N, source contacts 464 and 478 are formed insource contact openings 458 and 465, respectively, (shown in FIG. 4M) atthe backside of P-type doped semiconductor layer 406. Source contact 464is above memory stack 430 and in contact with P-type doped semiconductorlayer 406, according to some embodiments. Source contact 478 is abovememory stack 430 and in contact with N-well 407, according to someembodiments. In some embodiments, one or more conductive materials aredeposited into source contact openings 458 and 465 using one or morethin film deposition processes, such as ALD, CVD, PVD, any othersuitable processes, or any combination thereof, to fill source contactopenings 458 and 465 with adhesive layers (e.g., TiN) and conductorlayers (e.g., W). A planarization process, such as CMP, can then beperformed to remove the excess conductive materials, such that the topsurfaces of source contacts 464 and 478 are flush with one another aswell as flush with the top surface of ILD layers 456. It is understoodthat in some examples, source contacts 464 and 478 may be formed by thesame deposition and CMP processes to reduce the number of fabricationprocesses.

Method 600 proceeds to operation 620, as illustrated in FIG. 6A, inwhich an interconnect layer is formed above and in contact with thefirst and second source contacts. In some embodiments, the interconnectlayer includes a first interconnect and a second interconnect above andin contact with the first and second source contacts, respectively.

As illustrated in FIG. 4O, a redistribution layer 470 is formed aboveand in contact with source contacts 464 and 478. In some embodiments,redistribution layer 470 is formed by depositing a conductive material,such as Al, on the top surfaces of ILD layers 456 and source contact 364using one or more thin film deposition processes, such as ALD, CVD, PVD,any other suitable processes, or any combination thereof. In someembodiments, redistribution layer 470 is patterned by lithography andetching processes to form a first interconnect 470-1 above and incontact with source contact 464 and a second interconnect 470-2 aboveand in contact with source contact 478. First and second interconnects470-1 and 470-2 can be electrically separated from one another. Apassivation layer 472 can be formed on redistribution layer 470. In someembodiments, passivation layer 472 is formed by depositing a dielectricmaterial, such as silicon nitride, using one or more thin filmdeposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof. An interconnect layer 476including ILD layers 456, redistribution layer 470, and passivationlayer 472 is thereby formed, according to some embodiments.

As illustrated in FIG. 4L, contact openings 460, 461, and 463 eachextending through ILD layers 456 and P-type doped semiconductor layer406 are formed. In some embodiments, contact openings 460, 461, and 463are formed using wet etching and/or dry etching, such as RIE, throughILD layers 456 and P-type doped semiconductor layer 406. In someembodiments, contact openings 460, 461, and 463 are patterned usinglithography to be aligned with peripheral contacts 438, 440, and 439,respectively. The etching of contact openings 460, 461, and 463 can stopat the upper ends of peripheral contacts 438, 439, and 440 to exposeperipheral contacts 438, 439, and 440. The etching of contact openings460, 461, and 463 can be performed by the same etching process to reducethe number of etching processes. It is understood that due to thedifferent etching depths, the etching of contact openings 460, 461, and463 may be performed prior to the etching of source contact opening 465,or vice versa, but not at the same time.

As illustrated in FIG. 4M, a spacer 462 is formed along the sidewalls ofcontact openings 460, 461, and 463 as well as source contact opening 465to electrically separate P-type doped semiconductor layer 406 using oneor more thin film deposition processes, such as ALD, CVD, PVD, any othersuitable processes, or any combination thereof. In some embodiments,spacers 462 are formed along the sidewalls of contact openings 460, 461,and 463 as well as source contact opening 465 by the same depositionprocess to reduce the number of fabrication processes. In someembodiments, the etching of source contact opening 458 is performedafter the formation of spacer 362, such that spacer 362 is not formedalong the sidewall of source contact opening 358 to increase the contactarea between source contact 364 and N-type doped semiconductor layer306.

As illustrated in FIG. 4N, contacts 466, 468, and 469 are formed incontact openings 460, 461, and 463, respectively (shown in FIG. 4M) atthe backside of P-type doped semiconductor layer 406. Contacts 466, 468,and 469 extend vertically through ILD layers 456 and P-type dopedsemiconductor layer 406, according to some embodiments. Contacts 466,468, and 469 as well as source contacts 464 and 478 can be formed usingthe same deposition process to reduce the number of depositionprocesses. In some embodiments, one or more conductive materials aredeposited into contact openings 460, 461, and 463 using one or more thinfilm deposition processes, such as ALD, CVD, PVD, any other suitableprocesses, or any combination thereof, to fill contact openings 460,461, and 463 with an adhesive layer (e.g., TiN) and a conductor layer(e.g., W). A planarization process, such as CMP, can then be performedto remove the excess conductive materials, such that the top surfaces ofcontacts 466, 468, and 469 (and the top surfaces of source contact 464and 478) are flush with the top surface of ILD layers 456. In someembodiments, as contact openings 460, 461, and 463 are aligned withperipheral contacts 438, 440, and 439, respectively, contacts 466, 468,and 469 are above and in contact with peripheral contacts 438, 440, and439, respectively, as well.

As illustrated in FIG. 4O, first interconnect 470-1 of redistributionlayer 470 is formed above and in contact with contact 466. As a result,P-type doped semiconductor layer 406 can be electrically connected toperipheral contact 438 through source contact 464, first interconnect470-1 of interconnect layer 476, and contact 466. In some embodiments,P-type doped semiconductor layer 406 is electrically connected toperipheral circuits 452 through source contact 464, first interconnect470-1 of interconnect layer 476, contact 466, peripheral contact 438,and bonding layers 446 and 448. Similarly, second interconnect 470-2 ofredistribution layer 470 is formed above and in contact with contact469. As a result, N-well 407 can be electrically connected to peripheralcontact 438 through source contact 478, second interconnect 470-2 ofinterconnect layer 476, and contact 469. In some embodiments, N-well 407is electrically connected to peripheral circuits 452 through sourcecontact 478, second interconnect 470-2 of interconnect layer 476,contact 469, peripheral contact 439, and bonding layers 446 and 448.

As illustrated in FIG. 4O, a contact pad 474 is formed above and incontact with contact 468. In some embodiments, part of passivation layer472 covering contact 468 is removed by wet etching and/or dry etching toexpose part of redistribution layer 470 underneath to form contact pad474. As a result, contact pad 474 for pad-out can be electricallyconnected to peripheral circuits 452 through contact 468, peripheralcontact 440, and bonding layers 446 and 448.

It is understood that the second substrate, sacrificial layer, andP-type doped semiconductor layer described above in method 600 may bereplaced by an SOI wafer, which includes a handling layer, a buriedoxide layer (also known as a “BOX” layer), and a device layer asdescribed below with respect to method 601. The detail of similaroperations between methods 600 and 601 may not be repeated for ease ofdescription. Referring to FIG. 6B, method 601 starts at operation 602,in which a peripheral circuit is formed on a first substrate. The firstsubstrate can be a silicon substrate.

Method 601 proceeds to operation 603, as illustrated in FIG. 6B, inwhich a device layer of an SOI wafer is doped with a P-type dopant. TheSOI wafer can include a handling layer, a buried oxide layer, and adevice layer. In some embodiments, the buried oxide layer includessilicon oxide, and the device layer includes single crystalline silicon.Method 601 proceeds to operation 605, as illustrated in FIG. 6B, inwhich part of the doped device layer is doped with an N-type dopant toform an N-well in the doped device layer.

As illustrated in FIG. 4A, an SOI wafer 401 includes a handling layer402 (corresponding to carrier substrate 402 above in describing method600), a buried oxide layer 404 (corresponding to sacrificial layer 404),and a device layer 406 (corresponding to P-type doped semiconductorlayer 406). Device layer 406 can be doped with P-type dopant(s), such asP, As, or Sb, using ion implantation and/or thermal diffusion to becomea P-type doped device layer 406. Part of doped device layer 406 can befurther doped with N-type dopant(s), such as B, Ga, or Al, using ionimplantation and/or thermal diffusion to form N-well 407. It isunderstood that the above descriptions related to carrier substrate 402,sacrificial layer 404, and P-type doped semiconductor layer 406 can besimilarly applied to handling layer 402, buried oxide layer 404, anddoped device layer 406 of SOI wafer 401, respectively, to betterunderstand method 601 below and thus, are not repeated for ease ofdescription.

Method 601 proceeds to operation 607, as illustrated in FIG. 6B, inwhich a dielectric stack is formed on the doped device layer of the SOIwafer. The dielectric stack can include interleaved stack dielectriclayers and stack sacrificial layers. Method 601 proceeds to operation609, as illustrated in FIG. 6B, in which a channel structure extendingvertically through the dielectric stack and the doped device layer isformed. In some embodiments, to form the channel structure, a channelhole extending vertically through the dielectric stack and the dopeddevice layer, stopping at the buried oxide layer, is formed, and amemory film and a semiconductor channel are subsequently deposited alonga sidewall of the channel hole. Method 601 proceeds to operation 608, asillustrated in FIG. 6B, in which the dielectric stack is replaced with amemory stack, such that the channel structure extends vertically throughthe memory stack and the doped device layer. In some embodiments, toreplace the dielectric stack with the memory stack, an opening extendingvertically through the dielectric stack is etched, stopping at the dopeddevice layer, and the stack sacrificial layers are replaced with stackconductive layers through the opening to form the memory stack includinginterleaved the stack dielectric layers and the stack conductive layers.Method 601 proceeds to operation 610, as illustrated in FIG. 6B, inwhich an insulating structure extending vertically through the memorystack is formed. In some embodiments, to form the insulating structure,after forming the memory stack, one or more dielectric materials aredeposited into the opening to fill the opening.

Method 601 proceeds to operation 613, as illustrated in FIG. 6B, inwhich the first substrate and the SOI wafer are bonded in a face-to-facemanner, such that the memory stack is above the peripheral circuit. Thebonding can include hybrid bonding. Method 601 proceeds to operation615, as illustrated in FIG. 6B, in which the handle layer and the buriedoxide layer of the SOI wafer are removed to expose an end of the channelstructure. Method 601 proceeds to operation 617, as illustrated in FIG.6B, in which part of the channel structure abutting the doped devicelayer is replaced with a semiconductor plug. In some embodiments, toreplace the part of the channel structure abutting the doped devicelayer with the semiconductor plug, part of the memory film abutting thedoped device layer is etched to form a recess surrounding part of thesemiconductor channel, the part of the semiconductor channel is doped,and polysilicon is deposited into the recess to form the semiconductorplug surrounding and in contact with the part of the doped semiconductorchannel.

Method 601 proceeds to operation 619, as illustrated in FIG. 6B, inwhich a first source contact above the memory stack and in contact withthe doped device layer is formed, and a second source contact above thememory stack and in contact with the N-well is formed. Method 601proceeds to operation 621, as illustrated in FIG. 6B, in which aninterconnect layer above and in contact with the first and second sourcecontacts is formed. In some embodiments, the interconnect layer includesa first interconnect above and in contact with the first source contact,and a second interconnect above and in contact with the second sourcecontact. In some embodiments, a first contact is formed through thedoped device layer and in contact with the first interconnect, such thatthe doped device layer is electrically connected to the first contactthrough the first source contact and the first interconnect. In someembodiments, a second contact is formed through the doped device layerand in contact with the second interconnect, such that the N-well iselectrically connected to the second contact through the second sourcecontact and the second interconnect.

According to one aspect of the present disclosure, a method for forminga 3D memory device is disclosed. A sacrificial layer on a substrate, anN-type doped semiconductor layer on the sacrificial layer, and adielectric stack on the N-type doped semiconductor layer aresubsequently formed. A channel structure extending vertically throughthe dielectric stack and the N-type doped semiconductor layer is formed.The dielectric stack is replaced with a memory stack, such that thechannel structure extends vertically through the memory stack and theN-type doped semiconductor layer. The substrate and the sacrificiallayer are removed to expose an end of the channel structure. Part of thechannel structure abutting the N-type doped semiconductor layer isreplaced with a semiconductor plug.

In some embodiments, the substrate is a carrier substrate, thesacrificial layer includes a dielectric material, the N-type dopedsemiconductor layer includes polysilicon, and the dielectric stackincludes interleaved stack dielectric layers and stack sacrificiallayers.

In some embodiments, to replace the dielectric stack with the memorystack, an opening extending vertically through the dielectric stack isetched, stopping at the N-type doped semiconductor layer, and the stacksacrificial layers are replaced with stack conductive layers through theopening to form the memory stack including interleaved the stackdielectric layers and the stack conductive layers.

In some embodiments, after replacing the dielectric stack with thememory stack, one or more dielectric materials are deposited into theopening to form an insulating structure extending vertically through thememory stack.

In some embodiments, to form the channel structure, a channel holeextending vertically through the dielectric stack and the N-type dopedsemiconductor layer is etched, stopping at the sacrificial layer, and amemory film and a semiconductor channel are subsequently deposited alonga sidewall of the channel hole.

In some embodiments, to replace the part of the channel structureabutting the N-type doped semiconductor layer with the semiconductorplug, part of the memory film abutting the N-type doped semiconductorlayer is etched to form a recess surrounding part of the semiconductorchannel, the part of the semiconductor channel is doped, and polysiliconis deposited into the recess to form the semiconductor plug surroundingand in contact with the part of the doped semiconductor channel.

In some embodiments, after replacing the part of the channel structureabutting the N-type doped semiconductor layer with the semiconductorplug, a source contact in contact with the N-type doped semiconductorlayer is formed.

In some embodiments, an interconnect layer in contact with the sourcecontact is formed.

In some embodiments, a contact through the N-type doped semiconductorlayer and in contact with the interconnect layer is formed, such thatthe N-type doped semiconductor layer is electrically connected to thecontact through the source contact and the interconnect layer.

According to another aspect of the present disclosure, a method forforming a 3D memory device is disclosed. A device layer of an SOI waferincluding a handle layer, a buried oxide layer, and the device layer isdoped with an N-type dopant. A dielectric stack is formed on the dopeddevice layer of the SOI wafer. A channel structure extending verticallythrough the dielectric stack and the doped device layer is formed. Thedielectric stack is replaced with a memory stack, such that the channelstructure extends vertically through the memory stack and the dopeddevice layer. The handle layer and the buried oxide layer of the SOIwafer are removed to expose an end of the channel structure. Part of thechannel structure abutting the doped device layer is replaced with asemiconductor plug.

In some embodiments, the dielectric stack includes interleaved stackdielectric layers and stack sacrificial layers. In some embodiments, toreplace the dielectric stack with the memory stack, an opening extendingvertically through the dielectric stack is etched, stopping at the dopeddevice layer, and the stack sacrificial layers are replaced with stackconductive layers through the opening to form the memory stack includinginterleaved the stack dielectric layers and the stack conductive layers.

In some embodiments, after replacing the dielectric stack with thememory stack, one or more dielectric materials are deposited into theopening to form an insulating structure extending vertically through thememory stack.

In some embodiments, to form the channel structure, a channel holeextending vertically through the dielectric stack and the doped devicelayer is etched, stopping at the buried oxide layer, and a memory filmand a semiconductor channel are subsequently deposited along a sidewallof the channel hole.

In some embodiments, to replace the part of the channel structureabutting the doped device layer with the semiconductor plug, part of thememory film abutting the doped device layer is etched to form a recesssurrounding part of the semiconductor channel, the part of thesemiconductor channel is doped, and polysilicon is deposited into therecess to form the semiconductor plug surrounding and in contact withthe part of the doped semiconductor channel.

In some embodiments, after replacing the part of the channel structureabutting the doped device layer with the semiconductor plug, a sourcecontact in contact with the doped device layer is formed.

In some embodiments, an interconnect layer in contact with the sourcecontact is formed.

In some embodiments, a contact is formed through the doped device layerand in contact with the interconnect layer, such that the doped devicelayer is electrically connected to the contact through the sourcecontact and the interconnect layer.

According to still another aspect of the present disclosure, a methodfor forming a 3D memory device is disclosed. A peripheral circuit isformed on a first substrate. A channel structure extending verticallythrough a memory stack and an N-type doped semiconductor layer is formedabove a second substrate. The first substrate and the second substrateare bonded in a face-to-face manner, such that the memory stack is abovethe peripheral circuit. The second substrate is removed to expose anupper end of the channel structure. Part of the channel structureabutting the N-type doped semiconductor layer is replaced with asemiconductor plug.

In some embodiments, to form the channel structure, a dielectric stackis formed on the N-type doped semiconductor layer, the channel structureextending vertically through the dielectric stack and the N-type dopedsemiconductor layer is formed, and the dielectric stack is replaced withthe memory stack.

In some embodiments, to form the channel structure, a channel holeextending vertically through the dielectric stack and the N-type dopedsemiconductor layer is etched, and a memory film and a semiconductorchannel are subsequently deposited along a sidewall of the channel hole.

In some embodiments, to replace the part of the channel structureabutting the N-type doped semiconductor layer with the semiconductorplug, part of the memory film abutting the N-type doped semiconductorlayer is etched to form a recess surrounding part of the semiconductorchannel, the part of the semiconductor channel is doped, and polysiliconis deposited into the recess to form the semiconductor plug surroundingand in contact with the part of the doped semiconductor channel.

In some embodiments, prior to bonding the first substrate and the secondsubstrate, an insulating structure extending vertically through thememory stack is formed.

In some embodiments, after replacing the part of the channel structureabutting the N-type doped semiconductor layer with the semiconductorplug, a source contact above the memory stack and in contact with theN-type doped semiconductor layer is formed.

In some embodiments, an interconnect layer above and in contact with thesource contact is formed.

In some embodiments, a contact through the N-type doped semiconductorlayer and in contact with the interconnect layer is formed, such thatthe N-type doped semiconductor layer is electrically connected to thecontact through the source contact and the interconnect layer.

In some embodiments, the bonding includes hybrid bonding.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for forming a three-dimensional (3D)memory device, comprising: forming a semiconductor layer; forming amemory stack on the semiconductor layer; forming a channel structureextending through the memory stack and the semiconductor layer; exposingan end of the channel structure abutting the semiconductor layer; andreplacing a portion of the channel structure abutting the semiconductorlayer with a semiconductor plug.
 2. The method of claim 1, furthercomprising: forming a sacrificial layer on a carrier substrate, whereinthe semiconductor layer is formed on the sacrificial layer; and removingthe carrier substrate and the sacrificial layer to expose the end of thechannel structure abutting the semiconductor layer.
 3. The method ofclaim 1, further comprising forming a source contact connected to thesemiconductor layer after replacing the portion of the channel structureabutting the semiconductor layer with the semiconductor plug.
 4. Themethod of claim 3, wherein the semiconductor layer is an N-type dopedsemiconductor layer; and the source contact and the memory stack aredisposed at opposites sides of the N-type doped semiconductor layer, andthe source contact extends into the N-type doped semiconductor layer andis in contact with the N-type doped semiconductor layer.
 5. The methodof claim 3, wherein the semiconductor layer is a P-type dopedsemiconductor layer comprising an N-well; the source contact and thememory stack are disposed at opposites sides of the P-type dopedsemiconductor layer; and the source contact comprises a first sourcecontact and a second source contact, wherein the first source contactextends into the P-type doped semiconductor layer and is directly incontact with the P-type doped semiconductor layer, the second sourcecontact extends into the N-well and is directly in contact with theN-well.
 6. The method of claim 5, further comprising doping, with anN-type dopant, a part of the P-type doped semiconductor layer to formthe N-well arranged in the P-type doped semiconductor layer afterforming the P-type doped semiconductor layer.
 7. The method of claim 1,wherein forming the memory stack comprises: forming a dielectric stackcomprising interleaved stack dielectric layers and stack sacrificiallayers on the semiconductor layer; etching an opening extending throughthe dielectric stack, stopping at the semiconductor layer; and replacingthe stack sacrificial layers with stack conductive layers through theopening to form the memory stack.
 8. The method of claim 1, wherein thechannel structure comprises a memory film and a semiconductor channel;and replacing the portion of the channel structure abutting thesemiconductor layer with the semiconductor plug comprises: etching aportion of the memory film abutting the semiconductor layer to form arecess surrounding a portion of the semiconductor channel; doping theportion of the semiconductor channel exposed by the recess; anddepositing polysilicon into the recess to form the semiconductor plugsurrounding and in contact with the portion of the semiconductorchannel.
 9. The method of claim 3, further comprising: forming aninterconnect layer in contact with the source contact; and forming acontact through the semiconductor layer and in contact with theinterconnect layer, such that the semiconductor layer is connected tothe contact through the source contact and the interconnect layer.
 10. Amethod for forming a three-dimensional (3D) memory device, comprising:doping, with a dopant, a device layer of a silicon on insulator (SOI)wafer comprising a handle layer, a buried oxide layer, and the devicelayer to form a doped device layer; forming a memory stack on the dopeddevice layer; forming a channel structure extending through the memorystack and the doped device layer; removing the handle layer and theburied oxide layer of the SOI wafer to expose an end of the channelstructure; and replacing a portion of the channel structure abutting thedoped device layer with a semiconductor plug.
 11. The method of claim10, further comprising forming a source contact connected to the dopeddevice layer after replacing the portion of the channel structureabutting the doped device layer with the semiconductor plug.
 12. Themethod of claim 11, wherein the dopant is an N-type dopant; the sourcecontact and the memory stack are disposed at opposites sides of thedoped device layer, and the source contact extends into the doped devicelayer and is in contact with the doped device layer.
 13. The method ofclaim 11, wherein the dopant is a P-type dopant; the doped device layercomprises an N-well; the source contact and the memory stack aredisposed at opposites sides of the doped device layer; and the sourcecontact comprises a first source contact and a second source contact,wherein the first source contact extends into the doped device layer andis directly in contact with the doped device layer, the second sourcecontact extends into the N-well and is directly in contact with theN-well.
 14. The method of claim 13, further comprising doping, with anN-type dopant, a part of the doped device layer to form the N-wellarranged in the doped device layer after doping the device layer to formthe doped device layer.
 15. The method of claim 10, wherein forming thememory stack on the doped device layer comprises: forming a dielectricstack comprising interleaved stack dielectric layers and stacksacrificial layers on the doped device layer; etching an openingextending through the dielectric stack, stopping at the doped devicelayer; and replacing the stack sacrificial layers with stack conductivelayers through the opening to form the memory stack.
 16. The method ofclaim 10, wherein the channel structure comprises a memory film and asemiconductor channel; and replacing the portion of the channelstructure abutting the doped device layer with the semiconductor plugcomprises: etching a portion of the memory film abutting the dopeddevice layer to form a recess surrounding a portion of the semiconductorchannel; doping the portion of the semiconductor channel exposed by therecess; and depositing polysilicon into the recess to form thesemiconductor plug surrounding and in contact with the portion of thesemiconductor channel.
 17. The method of claim 11, further comprising:forming an interconnect layer in contact with the source contact; andforming a contact through the doped device layer and in contact with theinterconnect layer, such that the doped device layer is connected to thecontact through the source contact and the interconnect layer.
 18. Amethod for forming a three-dimensional (3D) memory device, comprising:forming a first wafer comprising: a first substrate, and a peripheralcircuit on the first substrate; forming a second wafer comprising: asecond substrate, a semiconductor layer above the second substrate, amemory stack comprising interleaved layers of stack dielectric layersand stack conductive layers above the semiconductor layer, and a channelstructure extending through the memory stack and the semiconductorlayer; bonding the first wafer and the second wafer in a face-to-facemanner, such that the memory stack is above the peripheral circuit;removing the second substrate to expose an upper end of the channelstructure; and replacing a portion of the channel structure abutting thesemiconductor layer with a semiconductor plug.
 19. The method of claim18, further comprising prior to bonding the first wafer and the secondwafer, forming an insulating structure extending vertically through thememory stack.
 20. The method of claim 18, wherein the semiconductorlayer comprises an N-type doped semiconductor layer or a P-type dopedsemiconductor layer.